A    RESPIRATION    CALORIMETER 


WITH  APPLIANCES 


FOR  THE 


DIRECT  DETERMINATION  OF  OXYGEN 


BY 

W.  O.  ATWATER  and  F.  G.  BENEDICT 

OF  WESLEYAN  UNIVERSITY 


WASHINGTON,  D.  C.: 

Published  by  the  Carnegie  Institution  of  Washington 
1905 


CARNEGIE  INSTITUTION  OF  WASHINGTON 

PUBLICATION  No.  42 


WASHINGTON.  D.  C. 

PRESS  OF  JUDD  &  DETWEILER  (INC.) 

1905 


PREFACE. 


The  apparatus  to  be  described  in  this  report  has  been  in  process  of 
development  for  twelve  years.  During  this  time  the  resources  of  Wes- 
leyan  University  have  been  supplemented  by  appropriations  from  the 
United  States  Department  of  Agriculture  and  the  Connecticut  (Storrs) 
Agricultural  Experiment  Station,  and  by  contributions  from  private 
individuals.  In  aid  of  a  series  of  experiments  with  the  apparatus  in  its 
earlier  stages,  grants  from  the  Elizabeth  Thompson  Science  Fund  and 
the  Bache  Fund  were  obtained.  The  addition  of  the  apparatus  for  the 
determination  of  oxygen  was  made  possible  by  liberal  grants  from  the 
Carnegie  Institution  of  Washington. 

In  the  development  of  apparatus  necessarily  so  elaborate  as  this  the 
active  cooperation  of  a  skillful  instrument  builder  is  absolutely  essential. 
It  has  been  our  good  fortune  to  have  the  service  of  Mr.  S.  C.  Dinsmore, 
whose  mechanical  skill  has  insured  the  successful  operation  of  many 
parts  of  the  apparatus.  Dr.  Paul  Murrill,  formerly  associated  with 
this  research,  rendered  invaluable  assistance  in  devising  the  methods 
of  computation.  Mr.  R.  D.  Milnerand  Mr.  H.  L,.  Knight  have  assisted 
materially  in  the  preparation  of  this  report. 

Dr.  E.  B.  Rosa,  physicist  of  the  National  Bureau  of  Standards,  but 
previously  professor  of  physics  at  Wesleyan  University,  was  actively 
engaged  in  this  investigation  in  its  earlier  stages  and  has  subsequently 
from  time  to  time  given  advice  which  has  assisted  greatly  in  the 
furtherance  of  the  work. 

The  first  grant  of  the  Carnegie  Institution  for  the  development  of 
the  apparatus  for  the  direct  determination  of  oxygen  was  made  to  my 
colleague,  Prof.  W.  O.  Atwater.  It  was  then  expected  that  the  report 
containing  the  description  of  the  apparatus  would  be  issued  under  the 
joint  authorship  of  Professor  Atwater  and  the  writer.  It  has  been 
deemed  fitting,  therefore,  to  retain  his  name  on  the  title  page  of  this 
report.  A  serious  illness  has  compelled  his  untimely  retirement  from 
the  work,  and  the  writer,  who  has  had  the  personal  supervision  of  the 
development  of  the  apparatus  since  1895,  has  continued  the  research. 

Inasmuch  as  this  report  has  been  written,  some  of  the  apparatus 
herein  described  has  been  developed,  and  the  experiment  with  man  has 
been  carried  out  subsequent  to  Professor  Atwater's  retirement,  the  writer 
assumes  full  responsibility  for  this  report  as  it  stands,  and  against  him 
alone  should  adverse  criticism  be  directed. 

FRANCIS  GANG  BENEDICT. 
August,  1905. 

in 


CONTENTS. 


Page 

Introduction 1-4 

The  respiration  calorimeter 4-11 

Description  of  the  apparatus  in  its  earlier 

form 5 

Description    of   laboratory    and   arrange- 
ment of  apparatus 7 

The  respiration  apparatus 11-56 

General  principle II 

The  respiration  chamber 12 

Openings  in  the  chamber 13 

Window 13 

Food  aperture  14 

Air-pipe  openings 14 

Opening  for  weighing  apparatus 16 

Opening  for  the  water-pipes 16 

Rod  for  adjusting  position  of  shields..  17 

Electric-cable  tube 17 

Piping  and  valves  to  the  blower 17 

The  rotary  blower 18 

Mercury  valves 20 

Apparatus  for  the  determination  of  water..  23-27 

Collection  of  drip 23 

Removal  of  water  vapor  from  the  air  cur- 
rent   24 

Description  of  the  water-absorbers 24 

Durability  of  the  water-absorbers 26 

Efficiency  of  the  water-absorbers 26 

Supply  of  sulphuric  acid 27 

Apparatus  for  the  determination  of  carbon 

dioxide 27-31 

Description  of  the  carbon-dioxide  ab- 
sorbers   27 

Vise  for  tightening  absorbers 28 

Removal  of  spent  soda  lime  from  the 

absorbers 29 

Preparation  of  soda  lime 29 

Efficiency  of  the  carbon-dioxide  ab- 
sorbers   30 

Testing  the  water  and  carbon-dioxide  ab- 
sorber system 32 

Maintenance  of  the  supply  of  oxygen 32 

Analysis  of  oxygen 34 

Preparation  of  the  reagents 37 

Converting  percentage  by  volume  to 

percentage  by  weight 38 

Computation  of  percentage  of  nitro- 
gen by  weight,  using  (actors 38 

The  tension  equalizers 39 

Calibration  of  the  pans 41 

Possibility  of  noxious  gases  in  the  system..  42 
Acid  fumes  carried  over  by  air  cur- 
rent   42 

Mercury  vapor  in  the  air 42 

Proportion  of  water  vapor  in  the  air..  43 


Page 

The  respiration  apparatus— Continued. 
Apparatus  for  the  analysis  of  the  residual 

air 44-56 

Apparatus  for  absorption  of  water 45 

Efficiency  of  absorption 45 

Apparatus  for  carbon-dioxide  absorption..    46 

Efficiency  of  absorption 46 

The  Elster  meter 46 

Calibration  of  Elster  meter 47 

Test  for  saturation  of  air  passing  through 

the  Els-ter  meter 47 

Apparatus  for  drawing  sample 48 

Apparatus  for  constant  water  pressure    50 

Process  of  taking  residual  samples.. 50 

Sampling  the  air  for  the  determination  of 

oxygen 51 

Method  of  sampling 52 

The  analysisof  air 53 

Accessory  apparatus 56-62 

Balances 56-58 

Analytical 56 

Balances  for  weighing  the  carbon- 
dioxide  and  water  absorbers,  oxy- 
gen cylinders,  etc 56 

Weights 58 

The  barometer 60 

Observation  of  temperature 61 

Calculation  of  results 63-95 

Amount  of  water  absorbed 63 

Amount  of  carbon  dioxide  absorbed 65 

Amount  of  oxygen  admitted 65 

Residual  analytical  data 66 

Data  for  the  rejection  of  air 67 

Corrections  for  variations  in  volume  and 

composition  of  residual  air 67-83 

Necessity  for  residual  analyses 67 

Possibility  of  leakage 68 

Factors  used  in  the  calculation  of  the  re- 
sidual analyses 69 

Volume  of  air  in  air-circuit 69 

Volume  in  chamber 69 

Volume  of  air  in  air-pipe  from  cham- 
ber, mercury  valves,  and  blower..    70 

Volume  of  air  in  water-absorbers 70 

Volume  of   air  in  carbon-dioxide   ab- 
sorbers     70 

Volume  of  remainder  of  air  system 71 

Volume  of  objects  in  the  chamber  not 

permanent 71 

Volume  in  an  alcohol  check  experiment    71 

Volume  in  experiments  with  man 72 

Fluctuations  in  the  air  volume 72 

Volume  in  the  pans 72 

Compression  of  air  in  absorbing  system.    73 


VI 


CONTENTS. 


Page 
Calculation  of  results— Continued. 

Correction  for  mercury  valve 74 

Increase  in  volume  of  the  water-absorb- 
ers   74 

Fluctuations  in  volume  of  the  carbon- 
dioxide  absorbers 74 

Interchange  of  air  through  the  food 

aperture 75 

Addition  of  nitrogen  with  the  oxygen..    77 

The  rejection  of  air 77 

The  respiratory  loss 79 

Subdivision  of  air  volumes 80 

Composition    gradient   of  air    in    the 

closed  circuit 81 

Data  used  in  calculating   relation  of 

weights  and  volumes  of  gases 82 

Calculation  of  residual  analyses 83-95 

Volume  of  the  sample 83 

Calculation  of  true  volume  of  sample 
for  determination  of  carbon  diox- 
ide and  water 85 

Calculation  of  the  true  volume  of  air  in 

the  closed  air-circuit 86 

Total  residual  water  vapor 87 

Total  residual  carbon  dioxide 87 

Oxygen  and  nitrogen 88 

The  nitrogen  in  the  system 88 

Calculations  for  nitrogen 89 

Calculations  for  total  residual  oxygen...    89 
Accuracy  of  calculations  of  the  residual 

amount  of  oxygen 91 

Thermal  gradient  inside  the  chamber..    91 
Conclusions  regarding  the  accuracy  of 

the  oxygen  computation.. 92 

Check  on  the  computation  method  of 

determining  oxygen 93 

Computation  -of  the  total  carbon-dioxide 
and  water  output  and  oxygen  in- 
take   93 

Total  carbon-dioxide  output 93 

Total  output  of  water  vapor 94 

Computation  for  total  intake  of  oxygen.    95 

Alcohol  check  experiments 96-105 

Kindof  alcohol  used 96 

Determination  of  specific  gravity 97 

Alcoholometric  tables 98 

Factors  for  the  actual  amounts  of  carbon 

dioxide,  water,  and  oxygen 98 

Alcohol  lamp 99 

Frequency  and  duration  of  experiments..  102 
Calculation  of  the  alcohol  check  experi- 
ments   102 

Determination  of  carbon  dioxide 103 

Determination  of  water 104 

The  computations  for  oxygen 104 

The  calorimeter  system  and  measurements 

of  heat 106-169 

General  principle  of  the  calorimeter 106 

The  calorimeter  chamber 107 

"Wooden  walls  surrounding  the  chamber 107 

Air-spaces  and  heat  insulation m 


Page 

The  calorimeter  system  and  measurements 
of  heat— Continued. 

Facilities  for  removing  metal  chamber 112 

Methods  of  preventing  gain  or  loss  of  heat 

to  the  chamber 112-123 

Prevention  of  gain  or  loss  through  the 

metal  walls 112 

The  thermo-electric  elements 113 

Construction  of  the  elements 113 

Method  of  installing  elements 113 

Distribution  of  elements 115 

Electrical  connection  of  the  elements.  116 

Heating  and  cooling  the  air-space 117 

Healing  circuits 117 

Cooling  circuits 118 

Temperature  regulations  in  the  outer 

air-space 119 

Gain  or  loss  of  heat  through  openings  in 

the  chamber 120 

Gain  or  lossof  heat  through  theair  current .  122 

Measurement  of  heat 123-150 

The  heat-absorbing  system 123 

Regulation  of  rate  of  absorption  of  heat.  125 

Supply  of  water  for  measuring  heat 126 

Water  coolers 126 

Water  meter 126 

Calibration  of  the  meter 132 

Accuracy  of  the  meter 132 

Check  measurements  of  the  accuracy 

of  the  meter 133 

Thermometers  for  measuring   tempera- 
ture of  water 133 

Correction  for  pressure  of  water  on  the 

mercury  bulb 134 

Measurement  of  temperature  of  the  calo- 
rimeter   134 

Observer's  table 136 

Electrical  connections  on  the  table 138 

Mercury  switch  and  bridge 139 

Determination    of  the   quantity   of  heat 

eliminated 150-169 

Latent  heat  of  water  vapor 150 

Sensible  heat  removed  in  water  current...  151 

Unit  of  heat 151 

Calculation  of  the  quantity  measured...  151 
Corrections  to  measurements  of  heat  152-167 
The  hydrothermal  equivalent  of  the 

calorimeter 152 

Corrections  for  temperature  of  food  and 

dishes 153 

Adiabatic  cooling  of  gases 154 

Correction  for  heat    absorbed  by  bed 

and  bedding 154 

Correction  for  change  of  body  tempera- 
ture and  body  weight 155 

Measurement  of  body  temperature...  156 
Weighing  objects  inside  the  chamber..  157 
Description  of  weighing  apparatus...  158 

Weighing  the  absorbing  system 161 

Routine  of  the  weighings 163 

Checks  on  the  accuracy 164 


CONTENTS. 


VII 


Page 

The  calorimeter  system  and  measurements 
of  heat — Continued. 

The  ergometer 164 

Correction  for  the  magnetization  of 

the  fields  of  the  ergometer. 166 

Blanks  used  for  heat  records 166 

Tests  of  the  accuracy  of  the  heat-measuring 

apparatus 169-176 

Electrical  check  tests 169-174 

Electrical  unit  used , 171 

Length  and  duration  of  experiments 173 

Results  of  electrical  check  experiments...  174 
The  combustion  of  ethyl  alcohol  as  a  check 

on  the  heat  measurements 174-176 

Heat  of  combustion  of  alcohol 175 

Results  of  alcohol  check  experiment 176 

Experiment  with  man 177-193 

Measurement   of  intake  and  output  of 

material 177 

Measurement  of  intake  and  output  of 

energy 178 


Page 
Experiment  with  man — Continued. 

Analytical  methods _ 178 

Metabolism  experiment  No.  70 178-193 

Subject.... 178 

Food 179 

Routine  of  experiment 179 

Statistics  of  food,  feces,  and  urine 180 

Statistics  of  water  eliminated 181 

Statistics  of  carbon  dioxide  eliminated...  182 

Statistics  of  oxygen  consumed 183 

Respiratory  quotient.- 184 

Summary     of     calorimetric     measure- 
ments   185 

Intake  and  output  of  material  and  en- 
ergy.    187 

Gains  and  losses  of  body  material.™ 187 

Body  weight 190 

Intake  and  output  of  energy 190 

Calculations  of  energy  of  body  material 

gained  and  lost 193 

Conclusion 193 


ILLUSTRATIONS. 


Page 

FIG.    i.  General  plan  of  the  respiration  calorimeter  laboratory 8 

2.  The  laboratory  room.     View  from  southeast  corner 10 

3.  The  laboratory  room.     View  from  east  side 10 

4.  The  laboratory  room.     View  from  near  sink 10 

5.  The  laboratory  room.     View  from  alcove 10 

6.  Diagram  of  the  circulation  of  air  through  the  respiration  apparatus.  n 

7.  Interior  of  the  respiration  chamber 12 

8.  Horizontal  section  of  respiration  calorimeter  chamber 15 

9.  Rotary  blower 16 

10.  Mercury  valves 21 

1 1 .  Water-absorbers 26 

12.  A  carbon-dioxide  absorber 26 

13.  Cross-section  of  carbon-dioxide  absorber 28 

14.  Vise  for  tightening  carbon-dioxide  absorbers 32 

15.  An  oxygen  cylinder  with  valve,  rubber  pressure  bag,  and  purifying 

attachments 32 

16.  Apparatus  for  analysis  of  oxygen  and  air 32 

17.  Pans  for  equalizing  pressure 44 

18.  Apparatus  for  analysis  of  residual  air 44 

19.  Apparatus  for  drawing  sample  of  air  for  residual  analysis 49 

20.  Water-pressure  system 51 

21.  Balance  for  weighing  absorbers  and  oxygen  cylinders 58 

22.  Alcohol  lamp  and  connections loo 

23.  Vertical  cross-section  of  calorimeter  chamber  through  the  end 109 

24.  Vertical  (side)  cross-section  of  calorimeter  chamber no 

25.  Rear  view  of  calorimeter  chamber no 

26.  A  thermo-electric  element 114 

27.  Thermo-electric  element  mounted  on  wooden  rod 114 

28.  Method  of  installing  thermo-electric  elements  in  metal  walls 114 

29.  Side  view  of  metal  chamber  rolled  out  on  tracks 116 

30.  Front  view  of  metal  chamber  removed  from  wooden  casing 116 

31.  Details  of  interior  of  wooden  casing 118 

32.  Sectional  view  of  walls  of  chamber,  showing  method  of  installing 

air-pipes,  water-pipes,  and  rod  for  raising  and  lowering  shields.  124 

33.  Interior  of  respiration  calorimeter  chamber 124 

34.  The  water-meter 126 

35.  The  water-meter.     Diagrammatic  sections  showing  front  and  side 

views 128 

36.  Clutch  to  regulate  tension  on  water-meter 130 

37.  Observer's  table 136 

38.  Electrical  connections  on  observer's  table 138 

39.  A  unit  key  of  the  mercury  switch 140 

40.  The  mercury  switch,  top  removed 140 

41.  A  general  view  of  mercury  switch 140 

42.  Under  side  of  mercury  switch  showing  electrical  connections 140 

43.  Diagram  of  electrical  connections  of  mercury  switch 142 

44.  Diagram  of  simple  form  of  Wheatstone  bridge 144 

45.  The  rectal  thermometer 156 

46.  Weighing  apparatus  for  objects  inside  the  chamber 159 

47-  The  bicycle  ergometer 164 

48.  The  electric  counter 164 

49.  Connections  for  an  electrical  check  experiment 170 

IX 


A  RESPIRATION  CALORIMETER,  WITH  APPLIANCES  FOR 
THE  DIRECT  DETERMINATION  OE  OXYGEN. 


BY  W.  O.  ATWATER  AND  F.  G.  BENEDICT. 


INTRODUCTION. 

For  a  proper  understanding  of  the  metabolism  or  transformations  of 
matter  and  energy  in  the  body,  a  knowledge  of  both  total  income  and 
total  outgo  is  indispensable.  Physiologists  and  physicians  have  long 
been  accustomed  to  depend  very  largely  upon  data  from  the  analysis  of 
urine  for  information  regarding  the  metabolism  of  matter,  especially 
of  proteid,  in  the  body.  In  many  cases,  aside  from  gross  or  approxi- 
mate estimates  of  the  quantities  of  food  ingested,  they  made  no  attempt 
to  determine  the  income,  and  the  outgo  of  material  in  the  feces  was,  as 
a  rule,  entirely  neglected.  In  a  study  of  the  metabolism  of  proteid  in 
the  body  the  analyses  of  the  urine  have  a  very  great  significance,  which 
in  the  light  of  recent  researches,  such  as  those  of  Folin1  and  Burian,'is 
becoming  even  more  intelligently  comprehended.  But  it  has  been  long 
understood  that  many  other  transformations  of  matter  besides  those 
in  which  the  element  nitrogen  is  involved  occur  in  the  body,  for  the 
proper  study  of  which  a  knowledge  of  the  income  of  carbon,  hydrogen, 
oxygen,  water,  and  mineral  matters,  in  addition  to  that  of  nitrogen,  is 
necessary  ;  and,  since  the  disintegration  of  the  proteids  as  well  as  of 
the  fats  and  carbohydrates  of  the  body  is  accompanied  by  an  absorp- 
tion of  oxygen  from  the  air  and  an  elimination  of  carbon  dioxide  and 
water,  our  knowledge  of  the  outgo  must  include  not  only  the  quantity 
of  nitrogen  in  the  urine,  but  also  the  amounts  of  carbon  dioxide  and 
water  excreted  by  the  lungs  and  skin,  and  of  the  carbon,  hydrogen, 
oxygen,  and  mineral  matters  of  both  urine  and  feces. 

Furthermore,  for  many  purposes  the  measurement  of  intake  and 
output  of  matter  is  not  wholly  sufficient,  but  must  be  supplemented 
by  determinations  of  the  transformations  of  energy,  because  one  of  the 
chief  functions  of  food  is  to  supply  the  body  with  energy.  Moreover, 
the  study  of  the  transformations  of  matter  is  rendered  more  complete 
and  intelligible  by  a  knowledge  of  the  transformations  of  energy. 

1  Amer.  Journ.  Physiol.  (1905),  13,  pp.  45-115. 
'Zeits.  f.  physiol.  Chem.  (1905),  43,  p.  532. 

IB 


2  A   RESPIRATION   CALORIMETER. 

Experiments  in  which  the  balance  of  income  and  outgo  of  nitrogen 
alone  is  determined  are  comparatively  simple.  The  intake  of  nitrogen  is 
that  in  the  food  and  drink  ;  and  since  it  is  commonly  accepted  by  physiol- 
ogists that  none  of  the  nitrogen  from  food  or  body  material  is  eliminated 
in  gaseous  form,  the  only  sources  of  output  which  are  ordinarily  con- 
sidered are  the  urine  and  feces.  Doubtless  because  of  the  ease  with 
which  such  experiments  may  be  conducted,  the  number  of  nitrogen 
metabolism  experiments  that  have  been  made  is  very  large. 

For  a  study  of  the  metabolism  of  fats  and  carbohydrates,  however,  an 
estimate  of  the  gaseous  output  of  the  respiratory  products,  i.  c. ,  carbon 
dioxide  and  water,  and  of  the  intake  of  oxygen,  is,  as  has  been  stated, 
also  necessary,  in  addition  to  the  analyses  of  food,  drink,  and  excreta. 
These  determinations  can  not  be  even  approximated  without  the  use  of 
apparatus  specially  constructed  for  the  purpose,  known  as  respiration 
apparatus,  which  is  usually  of  necessity  somewhat  complicated. 

For  the  determinations  of  income  and  outgo  of  energy,  which  is 
measured  in  terms  of  heat,  special  forms  of  apparatus,  designated  cal- 
orimeters, are  necessary,  and  these  are  likewise  complicated. 

Since  the  more  complete  metabolism  experiments  are  not  so  easily 
carried  on,  they  are  much  less  numerous  than  the  simpler  nitrogen 
metabolism  experiments ;  still  the  number  in  which  more  or  less  com- 
plete balances  of  income  and  outgo  of  matter,  or  energy,  or  even  both, 
have  been  determined  is  relatively  large,  and  several  different  forms  of 
respiration  apparatus  and  calorimeters  have  been  used.  It  is  not  pos- 
sible to  give  here  a  detailed  historical  review  of  the  development  of 
such  apparatus,  and  indeed  it  is  hardly  necessary,  as  extensive  bibli- 
ographies and  descriptions  have  been  published  elsewhere.  It  will  be 
sufficient  for  the  present  purpose  to  mention  these  and  to  point  out  the 
different  types  of  apparatus. 

Accounts  of  various  types  of  respiration  apparatus  have  been  com- 
piled by  Zuntz '  and  Jaquet.*  The  various  forms  of  apparatus  which 
are  of  sufficient  size  to  permit  study  of  the  respiratory  changes  in  man 
or  large  animals  may  be  divided  into  four  classes. 

In  the  first  class  the  subject  is  confined  in  a  closed  chamber  for 
varying  periods  of  time.  The  carbon-dioxide  content  of  the  air  is  de- 
termined at  the  beginning  and  again  at  the  end,  and  the  volume  of  the 
inclosed  space  being  known,  the  amount  of  carbon  dioxide  eliminated 
during  this  period  is  thereby  readily  calculated.  The  apparatus  of 
Chauveau*  and  Laulani^4  were  constructed  on  this  plan. 

1  Hermann's  Handbuch  der  Physiologic,  4,  part  2,  pp.  88-162. 
1  Ergeb.  der  Physiol.  (1903),  2,  part  i,  pp.  458-469. 
'  Traite"  de  Physique  Biologique,  1,  p.  744. 
4  ijle'ments  de  Physiologic,  p.  355. 


INTRODUCTION.  3 

The  second  type  of  apparatus  is  known  as  the  "closed  circuit." 
The  subject  is  placed  in  a  chamber  through  which  a  current  of  air  is 
passed.  The  air  leaving  the  chamber  is  purified  by  the  removal  of  the 
carbon  dioxide  (and  in  some  instances  water) ,  replenished  with  oxygen, 
and  returned  to  the  chamber.  This  type  of  apparatus  was  that  origi- 
nated by  Regnault  and  Reiset. *  It  has  been  further  developed  by  Hoppe- 
Seyler  and  Stroganow,2  and  in  principle  is  the  basis  of  the  apparatus 
to  be  described  later  in  this  report.  This  method  permits  of  the  deter- 
mination of  carbon  dioxide,  water,  and  oxygen. 

A  third  form  of  respiration  apparatus  is  that  known  as  the  "open 
circuit."  The  subject  is  placed  in  a  closed  chamber  through  which  a 
current  of  air  is  drawn,  the  incoming  and  outgoing  air  being  analyzed. 
This  type  of  apparatus  was  first  brought  into  successful  use  by  Petten- 
kofer,3  and  was  afterward  elaborated  for  use  with  man  by  Sonden  and 
Tigers tedt,4  and  by  Atwater,  Woods,  and  Benedict.5 

It  is  interesting  to  note  that  Jaquet,6  by  using  a  modification  of  the 
apparatus  of  Fetter  son  for  exact  gas  analysis,  has  undertaken  the  deter- 
mination of  oxygen  consumed  by  man  in  an  "  open-circuit  "  apparatus. 

The  fourth  type  of  apparatus  is  used  primarily  for  short  experiments. 
By  means  of  appliances  attached  to  the  mouth  or  nose  the  subject  is 
supplied  with  normal  air  of  known  composition  and  the  products  of 
respiration  are  collected  for  analysis.  With  this  apparatus  it  is  possible 
to  determine  the  oxygen  absorbed  and  the  carbon  dioxide  exhaled. 
This  type  has  been  perfected  to  a  high  degree  by  Zuntz7  and  by  Chauveau 
and  Tissot.8 

The  development  of  calorimetric  apparatus  for  use  with  animals  and 
with  man  has  been  far  less  extensive  than  that  of  respiration  apparatus. 
A  summary  of  the  methods  and  results  of  experiments  on  the  income 
and  outgo  of  heat  of  the  animal  body,  which  includes  the  work  done  up 
to  about  1882,  was  published  by  Rosenthal.9  A  description  and  discus- 
sion of  more  recent  types  of  calorimeters  is  given  by  Laulanie,10  and  also 
by  Sigales.11  One  of  the  earliest  forms  suitable  for  use  with  man  and 
the  larger  animals  was  devised  by  Scharling12  in  1849.  The  subject 

1  Ann.  de  Chim.  et  Physique  (1849),  3,  xxvi. 

'Archiv.  f.  d.  ges.  Physiol.  (1876),  12,  p.  18. 

3  Ann.  der  Chem.  u.  Pharm.  (1862-3),  Supp.  2,  p.  17. 

4Skand.  Archiv.  f.  Physiol.  (1895),  6,  p.  I. 

5U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  44. 

6  Verhandlungen  der  naturforschenden  Gesellschaft  in  Basel,  15  (1904),  part  2, 
p.  252. 

7Berl.  klin.  Wchnschr.  (1887),  p.  429. 

8Comptes  rendus  (1899),  129,  p.  249. 

9  Hermann's  Handbuch  der  Physiologic,  4,  part  2,  pp.  289-456. 
10  Clements  de  Physiologic,  pp.  556-565. 
"Traite"  de  Physique  Biologique,  1,  pp.  816-843. 
12  Journ.  f.  prakt.  Chem.  (1849),  48,  p.  435. 


4  A    RESPIRATION   CALORIMETER. 

was  placed  in  a  closed  chamber  inside  a  larger  room  of  constant  tempera- 
ture. The  rise  in  temperature  of  the  inner  chamber  was  noted  and  the 
heat  emission  thereby  calculated.  Similar  types  have  been  those  of 
d'Arsonval,1  Him,2  and  Vogel.s 

The  newer  forms  are  of  two  types  :  First,  those  in  which  the  heat 
delivered  from  the  body  is  lost  through  the  walls  by  radiation  and  the 
calorimeter  calibrated  by  determining  the  radiation  constant ;  and, 
second ,  those  in  which  the  heat  developed  is  brought  away  by  a  cooling 
current  of  water  flowing  through  the  calorimeter  chamber,  the  radiation 
constant  being  eliminated  as  far  as  possible.  One  of  the  most  recent 
forms  of  the  first  type  of  apparatus  is  the  ' '  emission  ' '  calorimeter  of 
Chauveau ; 4  the  second  type  is  that  employed  originally  by  Atwater  and 
Rosa,5  and  in  its  more  developed  form  is  to  be  described  beyond. 

THE  RESPIRATION  CALORIMETER. 

As  has  been  stated,  the  more  satisfactory  experiments  are  those  in 
which  the  transformations  of  both  matter  and  energy  are  studied. 
For  such  experiments  it  is  essential  that  the  apparatus  used  be  so  con- 
structed as  to  afford  opportunity  for"  measuring  at  the  same  time  both 
the  respiratory  products  and  the  energy  given  off  from  the  body. 
Among  the  various  forms  of  apparatus  referred  to  in  the  preceding 
paragraphs  some  were  so  constructed,  and  such  is  especially  the  case 
with  the  apparatus  here  to  be  described.  To  indicate  its  twofold  func- 
tion as  a  respiration  apparatus  and  as  a  calorimeter,  it  is  designated  a 
"  respiration  calorimeter."  As  will  be  explained  in  detail,  the  respi- 
ration apparatus  is  of  the  ' '  closed-circuit ' '  type  of  Regnault  and 
Reiset ;  the  calorimeter  is  a  constant-temperature,  continuous-flow 
water  calorimeter. 

In  addition  to  the  measurements  of  respiratory  products  and  energy 
made  directly  by  the  apparatus,  the  experiments  include,  in  determi- 
nations of  matter,  the  analyses  of  the  air  in  the  apparatus  and  measure- 
ments of  the  amounts  of  oxygen  introduced,  and  the  weighing  and 
analyzing  of  the  food,  drink,  and  solid  and  liquid  excreta  ;  and  in  deter- 
minations of  energy  the  measurement  of  the  potential  energy,  i.  e., 
heats  of  oxidation,  of  the  solid  ingredients  of  food,  drink,  and  excreta. 
All  these  data  constitute  the  factors  of  total  income  and  outgo  of  both 
matter  and  energy. 

1  Soc.  de  Biol.  (1894),  27,  i. 

*Recherches  sur  1' Equivalent  mecanique  de  la  chaleur  (1858). 

3  Arch.  d.  Ver.  f.  wiss.  Heilk.  (1864),  p.  422. 

4Comptes  reudus  (1899),  129,  p.  249. 

5U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63. 


f 

DESCRIPTION.  5 

Many  of  the  forms  of  apparatus  previously  referred  to  were  designed 
for  experiments  with  lower  animals,  but  some  of  them  were  for  experi- 
ments with  man.  The  particular  apparatus  here  described  was  of  this 
latter  type  (though  it  can  be,  and  indeed  in  its  earlier  form  has  been, 
readily  adapted  for  use  with  domestic  animals) .  Experimenting  with 
man  necessarily  involves  certain  restrictions,  such  as  the  requirement 
of  a  varied  and  palatable  diet,  a  rate  of  ventilation  which  shall  insure 
proper  purification  of  the  air,  an  experimental  period  not  unduly  long, 
etc. ;  but  it  is  obvious  that  in  investigations  of  the  problems  of  nutri- 
tion of  man  it  is  a  decided  advantage  to  experiment  directly  with  man. 
Otherwise,  if  domestic  animals  were  used,  it  would  be  necessary  to  draw 
conclusions  for  omnivora  (man)  from  results  obtained  with  carnivora 
(dogs)  or  herbivora  (sheep  or  cattle).  Furthermore,  in  experimenting 
with  apparatus  as  elaborate  as  this  must  necessarily  be,  it  is  of  the 
greatest  value  to  have  the  intelligent  cooperation  of  the  subject  within 
the  apparatus  ;  and  the  fact  that  there  may  be  reasonable  control  of  the 
muscular  activity  and  sleep  is  also  an  advantage. 

As  will  be  seen  from  the  more  detailed  description  beyond,  the  cham- 
ber of  the  apparatus  is  large  enough  to  allow  a  man  to  stand  or  lie  down 
at  full  length,  and  to  move  about  to  a  limited  extent,  and  it  is  provided 
with  a  chair,  table,  and  bed,  that  may  be  folded  up  and  put  aside  when 
not  in  use,  so  that  the  subject  may  sit,  or  lie  down,  or  stand  and  move 
about  at  will,  or  as  the  conditions  of  the  experiment  prescribe.  When 
the  experiment  involves  muscular  work,  a  suitable  device  on  which 
work  may  be  performed,  and  by  means  of  which  the  amount  of  work 
done  may  be  determined,  is  also  provided.  A  window  in  one  end  of 
the  chamber  admits  ample  light  for  reading  and  writing,  and  as  it  faces 
a  window  in  the  laboratory,  even  allows  something  of  a  view  out  of 
doors.  A  telephone  affords  opportunity  for  communication  with  per- 
sons outside  the  apparatus.  The  air  is  kept  constantly  in  circulation, 
the  impurities  removed  from  it,  and  oxygen  restored  to  it.  The 
temperature  of  the  chamber  is  maintained  very  uniform,  whatever  the 
conditions  of  activity  of  the  subject.  Receptacles  for  food,  drink,  and 
excreta  are  introduced  or  removed  through  an  aperture  provided  for 
the  purpose.  Every  attempt  is  made  to  keep  the  subject  comfortable 
and  to  have  the  conditions  as  nearly  normal  as  possible. 

DESCRIPTION   OF  THE   APPARATUS   IN   ITS   EARLIER   FORM. 

The  respiration  calorimeter  at  Wesleyan  University  has  been  in  pro- 
cess of  development  about  twelve  years.  Several  publications  describ- 
ing the  earlier  form  of  apparatus,  with  modifications  and  improvements, 
and  reporting  the  experiments  made  with  it,  have  been  issued. 


6  A   RESPIRATION   CALORIMETER. 

An  account1  of  the  first  form  of  the  apparatus,  published  in  1897, 
consists  of  the  description  of  a  respiration  chamber  on  the  Pettenkofer 
principle,  the  arrangements  for  ventilating  the  same,  and  the  accessory 
apparatus  for  analyzing  the  air  of  the  chamber.  With  this  description 
was  included  a  report  of  four  experiments  in  which  the  intake  and 
output  of  nitrogen,  carbon  dioxide,  and  water  were  determined.  Satis- 
factory determinations  of  the  output  of  energy  by  means  of  the  apparatus 
were  not  yet  possible. 

In  1899  a  description 2  of  the  apparatus  in  its  next  stage  was  published. 
This  included  a  discussion  of  the  measurement  of  heat  eliminated  from 
the  body,  together  with  a  much  more  detailed  description  of  the  respi- 
ration chamber,  accessory  apparatus,  and  methods  of  manipulation  and 
analysis.  In  this  report  was  given  a  brief  account  of  two  experiments 
with  man  in  which  the  balance  of  intake  and  output  of  both  matter  and 
energy  was  determined. 

A  few  months  later  another  report,5  giving  a  detailed  description  of 
six  metabolism  experiments  with  men,  including  the  methods  of  calcu- 
lating and  interpreting  the  results,  was  published  ;  and  this  was  fol- 
lowed in  1 902  by  a  report 4  in  which  were  given  the  results  of  twenty- 
four  experiments  with  men  and  a  general  discussion  of  the  same.  A 
more  extensive  report &  of  the  results  of  twenty-six  more  experiments 
with  men  was  published  in  1903.  This  report  gives  also  an  account 
of  many  improvements  and  modifications  of  apparatus  that  had  been 
developed  in  the  course  of  the  experiments  ;  and  as  the  series  of  inves- 
tigations with  the  respiration  calorimeter  essentially  as  originally 
devised  was  completed,  considerable  discussion  of  general  principles 
and  deductions  based  upon  results  of  the  whole  six  years  of  experi- 
mentation was  included. 

In  addition  to  the  research  reported  in  the  publications  above  referred 
to,  the  apparatus  has  been  used  for  an  investigation  into  the  nutritive 
value  of  alcohol,  the  results  of  which  are  published  in  a  separate  report.' 
This  report  gives  the  detailed  description  and  discussion  of  the  results 
obtained  in  thirteen  experiments  with  men  in  which  alcohol  formed  a 
part  of  the  diet. 

None  of  the  experiments  above  referred  to,  however,  were  actually 
complete  metabolism  experiments,  for  the  reason  that  determinations  of 

1  U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  44. 

2  U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63. 

3  U.  S.  Dept.  of  Agr. ,  Office  of  Experiment  Stations  Bull.  69. 

*  U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  109. 

6U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  136. 

8W.  O.  Atwater  and  F.  G.  Benedict:  Mem.  Nat.  Acad.  Sci.  (1902),  8;  U.  S. 
Senate,  57th  Cong.,  first  sess.,  Doc.  233,  p.  231.  An  experimental  inquiry  on  the 
nutritive  value  of  alcohol. 


t 
DESCRIPTION.  7 

the  amounts  of  oxygen  consumed  could  not  be  made.  It  was  believed 
that  with  accurate  determinations  of  the  quantities  of  the  other  elements 
the  quantity  of  oxygen  consumed  could  be  approximately  estimated  by 
difference,  and  in  one  of  the  reports  above  mentioned  such  estimates 
were  made  according  to  the  method  elaborated  by  Rosa.1  It  is  obvi- 
ously much  more  desirable,  however,  to  be  able  to  make  the  oxygen 
determinations  directly,  the  same  as  those  of  the  other  elements.  As  a 
result  of  some  eight  years  of  experimenting  with  the  apparatus  above 
referred  to,  plans  were  gradually  evolved  for  attempting  the  measure- 
ment of  the  amount  of  oxygen  consumed  by  men,  and  thus  obtaining 
data  for  the  calculation  of  the  respiratory  quotient.  To  do  this  involved 
considerable  modification  of  the  form  of  apparatus  and  the  addition  of 
several  new  accessory  devices. 

Concurrently  with  the  devising  of  the  above  modifications,  many 
appliances  were  developed  to  insure  greater  accuracy  in  the  measure- 
ments of  heat  and  to  extend  the  range  of  the  calorimeter  sufficiently  to 
afford  means  of  measuring  heat  at  the  rate  of  600  calories  per  hour. 
These  fundamental  changes  extend  to  all  parts  of  the  respiration  calo- 
rimeter, which  is  consequently  so  modified  in  form  and  principle  from 
what  has  been  previously  described  as  to  render  it  a  new  apparatus  and 
to  call  for  a  new  description. 

It  is  the  purpose  of  the  present  publication,  therefore,  to  describe  in 
detail  the  respiration  calorimeter  as  now  used.  In  this  description  the 
two  functions  of  the  apparatus  will  be  treated  separately — first  the 
respiration  apparatus,  and  second  the  calorimeter.  Preliminary  to 
these  sections  is  a  description  of  the  laboratory  in  which  the  respira- 
tion calorimeter  is  installed. 

DESCRIPTION   OF    LABORATORY  AND    ARRANGEMENT    OP   APPARATUS. 

The  respiration  calorimeter  here  described  is  located  in  a  room  in  the 
northeast  corner  of  the  basement  of  a  large  stone  building,  known  as 
Orange  Judd  Hall,  of  Wesleyan  University,  at  Middletown,  Connecti- 
cut. The  north  and  east  sides  of  the  room  are  the  masonry  of  the 
building,  about  75  cm.  thick.  On  the  south  side  of  the  room  is  a  brick 
partition,  about  42  cm.  thick,  through  which  are  three  openings,  one 
with  a  door  opening  into  a  small  room,  and  the  other  two  leading  to 
an  alcove.  The  west  side  of  the  room  is  a  wooden  partition  with  a 
door  and  a  large  glass  window.  The  wooden  floor  is  laid  on  cement. 

There  are  three  windows  on  the  north  side,  about  130  cm.  wide  and 
150  cm.  high,  and  two  windows  on  the  east  side,  about  130  cm.  wide 

Physical  Review  (1900),  10,  p.  129. 


8 


A    RESPIRATION    CALORIMETER. 


and  185  cm.  high.  The  eastern  exposure  affords  direct  sunlight  until 
about  the  middle  of  the  morning.  After  that  time  the  direct  light 
does  not  enter,  but  the  room  is  excellently  lighted  and  the  walls  and 
ceiling  are  painted  white  to  aid  in  the  distribution  of  the  light. 


OBSERVERS 

,_..TAJ3LE 


AlCOVC. 


ALCOVt 


Fio.  i. -General  Plan  of  the  Respiration  Calorimeter  Laboratory. 


t 

DESCRIPTION.  9 

For  protection  against  severe  changes  of  external  temperature  during 
the  winter  months,  double  windows  are  provided.  The  room  is  heated 
by  steam-pipes  near  the  ceiling  and  by  gas  stoves.  Two  ventilating 
fans  belted  to  the  main  shaft  have  their  blades  so  adjusted  that  the 
warm  air  at  the  top  of  the  room  is  continually  forced  down.  It  is  pos- 
sible to  keep  the  temperature  of  the  room  comfortable  for  work,  but 
the  regulation  is  far  from  that  of  a  constant-temperature  room.  That 
accurate  calorimetric  work  can  be  done  in  a  room  with  such  an  uneven 
temperature  is  because  of  the  peculiar  construction  of  the  calorimeter, 
as  described  beyond.  The  general  plan  of  the  laboratory  room  is 
shown  in  figure  i. 

The  room  is  entered  by  the  door  near  the  southwest  corner.  The 
door  near  the  southeast  corner  leads  into  a  small  annex  used  for  a 
kitchen,  and  containing  ice-chests  and  tanks.  The  two  other  openings 
in  the  south  wall  lead  to  an  alcove  used  as  a  tool  and  supply  room. 

The  respiration  chamber  is  seen  in  about  the  middle  of  the  north 
side  of  the  laboratory,  separated  from  the  north  wall  by  an  air-space 
of  about  75  cm.  As  may  be  seen  in  figure  2,  the  wooden  walls  sur- 
rounding the  chamber  extend  from  floor  to  ceiling.  To  the  south  of 
the  respiration  chamber,  about  in  the  center  of  the  laboratory,  is  the 
long  table  on  which  are  the  rotary  blower  for  maintaining  a  current  of 
air  through  the  apparatus,  the  absorbers  for  removing  the  water  vapor 
and  carbon  dioxide  from  the  air  current,  and  the  appliances  for  the 
introduction  of  oxygen.  Suspended  from  the  ceiling  at  the  north 
side  of  the  laboratory  is  the  shafting  by  which  power  from  the  electric 
motors  on  the  west  side  is  transmitted  to  the  water-pump  and  the  rotary 
blower. 

The  small  table  at  the  west  of  the  chamber  is  convenient  for  the 
deposit  of  articles  to  be  passed  into  or  out  of  the  chamber  through  the 
aperture  just  above  it.  At  the  east  end  of  the  chamber  is  the  observer's 
table,  and  just  beside  this  is  the  water-meter.  Around  the  walls  of  the 
laboratory  at  convenient  points  are  desks,  tables,  balances,  sink,  etc. 
Near  the  door  entering  the  laboratory  is  a  barometer,  securely  attached 
to  stanchions  and  well  isolated  from  sudden  changes  in  temperature. 
The  rack  in  one  of  the  entrances  to  the  alcove  at  the  south  is  for  storing 
extra  carbon-dioxide  absorbers. 

The  disposition  of  the  apparatus  and  accessories  in  the  room  was 
made  with  a  view  to  facilitating  manipulation  and  to  conform  to  the 
previously  existing  shape  and  construction  of  the  laboratory  room, 
which  was  in  no  sense  peculiarly  adapted  for  calorimetric  work. 

A  general  view  of  the  laboratory  room,  taken  from  the  southeast 
window,  is  shown  in  figure  2. 


10  A   RESPIRATION   CALORIMETER. 

In  figure  2,  the  table  supporting  the  absorbing  system,  the  rotary 
blower,  and  the  apparatus  for  the  introduction  of  oxygen  appear  in  the 
center  of  the  foreground.  The  respiration  chamber  in  its  wooden  cas- 
ing, with  the  glass  door  in  the  east  end,  is  immediately  at  the  right,  and 
adjacent  thereto  are  the  observer's  table  and  water-meter.  The  air- 
pipes  conducting  air  to  and  from  the  respiration  chamber  are  suspended 
near  the  ceiling  and  extend  across  the  front  end  of  the  chamber.  At 
the  left,  securely  attached  to  the  brick  wall,  is  the  balance  for  weigh- 
ing the  absorbing  apparatus.  In  the  rear  and  immediately  at  the  right 
of  the  door  is  the  barometer  closet  attached  to  two  stanchions. 

Another  general  view  of  the  laboratory,  showing  more  of  the  detail 
of  the  respiration  chamber,  is  given  in  figure  3.  The  door  of  the  res- 
piration chamber  is  open,  thus  showing  a  little  of  the  interior.  The 
observer's  table,  water-meter,  and  galvanometer  hood  are  at  the  right, 
and  at  the  left  the  absorbing  apparatus,  rotary  blower,  and  balance  are 
shown. 

A  view  taken  from  near  the  sink,  figure  4,  shows  the  rear  end  of 
the  chamber.  In  the  center  of  this  end  of  the  chamber  is  the  opening 
through  which  the  food  and  excreta  are  passed,  shown  here  with  the 
outer  door  open.  On  the  table  immediately  beneath  it  are  character- 
istic vessels  used  to  introduce  or  remove  material  from  the  chamber. 
The  absorbing  system  is  shown  immediately  at  the  right.  On  the  end 
of  the  absorbing-system  table  are  seen  the  two  pans  with  rubber  dia- 
phragms (one  of  which  is  distended)  which  are  used  to  indicate  apparent 
changes  in  volume  of  air  in  the  whole  system.  Farther  at  the  right  is 
seen  the  water-pressure  regulator  standing  in  [the  arch  leading  to  the 
alcove  room  used  for  storing  apparatus. 

The  details  of  the  absorbing  system  are  better  shown  in  figure  5, 
which  was  taken  from  a  position  in  the  alcove  room  near  the  water- 
pressure  regulator  shown  in  figure  4.  The  smaller  of  the  two  pipes 
near  the  ceiling  at  the  right  conducts  the  air  from  the  respiration 
chamber  to  the  rotary  blower.  The  blower  forces  the  air  through  the 
absorbers  on  the  table.  The  air,  freed  from  carbon  dioxide  and  water 
vapor,  then  passes  upward  to  the  pipe  lying  on  the  top  shelf  of  the 
table,  to  which  the  two  pans  are  attached.  To  the  right  of  the  pans 
the  oxygen  is  supplied  to  the  air  in  this  pipe  from  the  cylinder  with  a 
large  U  tube  attached  to  it,  standing  upright  near  the  center  of  the  top 
shelf  of  the  table.  After  being  supplied  with  oxygen  the  air  proceeds 
along  the  horizontal  pipe  to  the  end  of  the  table,  where  it  passes  through 
the  vertical  section,  and  thence  along  the  ceiling  around  the  corner 
of  the  chamber,  entering  it  immediately  at  the  left  of  the  observer's 
table.  The  small  tubes  and  the  Elster  meter  at  the  right,  on  the  top 


To  face  page  10-1. 


FIG.  2.— The  Laboratory   Room.    View  from  southeast  corner.    Respiration  Chamber  at  right;  Water  and 
Carbon-Dioxide  Absorbing  System  in  center  ;  Balance  for  Weighing  Absorbers  at  left. 


FIG.  3. — Laboratory  Room.    View  from  east  side.    Observer's  Table  and  Water-Meter  in  foreground  ;  Window 
of  Respiration  Chamber  open  ;  Absorbing  System  and  Balance  at  left. 


TO  face  page  10-2. 


FIG.  4. — Laboratory  Room.    View  from  near  the  sink.    Rear  of  Respiration  Calorimeter  Chamber  showing  Food 
Aperture.    Absorbing  System  and  Pans  at  right. 


FIG.  5. — Laboratory  Room.     View  from  Alcove  near  Water-Pressure  Regulator.    Details  of  Absorbing  System, 
Klster  Meter  Connections,  Oxygen  Cylinder,  and  Pans. 


THE    RESPIRATION   APPARATUS. 


II 


shelf  of  the  table,  are  used  for  the  analysis  of  the  residual  air  in  the 
chamber. 

These  various  features  of  the  apparatus  are  described  in  more  detail 
beyond.  The  above  description  is  simply  to  afford  a  general  idea  of  the 
laboratory  and  apparatus  as  a  whole  before  the  more  specific  explanation 
is  undertaken. 

THE  RESPIRATION  APPARATUS. 
GENERAL   PRINCIPLE. 

The  respiration  apparatus  in  its  present  modified  form  is  constructed 
on  the  "  closed-circuit  "  plan.  It  consists  of  a  chamber  large  enough 
for  the  subject — a  man — to  live  in  comfortably,  and  ventilated'by  a  cur- 
rent of  air  which  is  kept  in  circulation  by  a  rotary  blower.  Provision 
is  made  for  purifying  the  ventilating  current  of  air,  which  is,  after  puri- 
fication, returned  to  the  chamber.  The  general  scheme  of  the  apparatus 
is  shown  diagrammatically  in  figure  6. 


RESPIRATION 
0  used 
H30 


CHAMBER 


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nt  rpducsd 


FlG.  6. — Diagram  of  Circulation  of  Air  through  Respiration  Apparatus. 

In  the  upper  portion  of  the  figure  the  respiration  chamber  is  shown, 
and  below  it  the  blower  and  absorbing  or  purifying  system.  Air  from 
the  chamber,  containing  nitrogen,  carbon  dioxide,  water  vapor,  and  a 
somewhat  diminished  percentage  of  oxygen,  passes  through  the  blower 
and  enters  the  absorbing  system.  Here  it  is  forced  through  sulphuric 
acid  to  remove  the  water  vapor,  and  through  a  specially  prepared  soda 
lime,  which  takes  out  the  carbon  dioxide.  The  soda  lime,  however, 
contains  water,  more  or  less  of  which  is  taken  up  by  the  air  current. 


12  A   RESPIRATION   CALORIMETER. 

The  air  is  therefore  again  forced  through  sulphuric  acid  (not  shown  in 
the  diagram)  and  then  enters  a  pipe  leading  back  to  the  chamber.  It 
is  now  freed  from  carbon  dioxide  and  water,  but  still  deficient  in  oxy- 
gen. The  oxygen  is  replenished  by  admitting  the  requisite  amount 
from  a  steel  cylinder  of  compressed  oxygen  through  an  opening  in  the 
ventilating  air-pipe,  as  shown  in  the  diagram,  and  the  air  when  restored 
to  a  respirable  condition  reenters  the  respiration  chamber. 

The  metal  walls  of  the  chamber  and  the  metal  pipes  confine  the  air 
in  a  definite  volume,  and  to  allow  for  expansion  or  contraction  of  the 
air  volume  as  the  result  of  barometric  or  thermometric  fluctuations  a 
compensating  device,  consisting  of  two  pans  with  flexible  rubber  covers, 
is  inserted  in  the  ventilating  air-pipe. 

The  amounts  of  water  and  carbon  dioxide  absorbed  by  the  sulphuric 
acid  and  soda  lime  and  of  oxygen  admitted  to  the  system  are  obtained 
by  direct  weighing  on  suitable  balances.  These  weights  give  an  approx- 
imate estimate  as  to  the  carbon  dioxide,  water,  and  oxygen  involved  in 
the  transformations  which  have  taken  place  in  the  body.  There  may 
be,  however,  considerable  variations  in  the  composition  of  the  air  in  the 
system  from  time  to  time,  especially  as  regards  the  oxygen  content, 
which  are  not  detected  in  this  way.  Since  the  volume  of  air  in  the 
closed  circuit  is  comparatively  large,  even  a  slight  variation  produces  a 
considerable  error.  It  is  therefore  necessary  to  know  the  composition 
of  the  air  at  the  beginning  of  an  experiment,  and  also  of  the  residual 
air  at  the  end  of  each  experimental  period.  Apparatus  suitable  for 
this  purpose  has  been  especially  devised  and  is  described  in  connection 
with  the  respiration  apparatus. 

From  these  data  as  a  whole,  with  suitable  corrections  to  be  explained 
in  detail,  it  is  possible  to  compute  accurately  the  amounts  of  oxygen 
absorbed  and  carbon  dioxide  and  water  eliminated  by  the  subject  during 
an  experiment. 

THE   RESPIRATION   CHAMBER. 

The  respiration  chamber  is  an  airtight,  constant-temperature  room, 
2.15  meters  long,  1.22  meters  wide,  and  1.92  meters  high,  with  a  total 
volume  of  about  5,000  liters.  It  is  lighted  by  a  window  on  the  east 
side,  and  has  several  other  openings  for  the  admission  and  removal  of 
food,  air,  etc.  It  is  furnished  with  a  table  and  bed,  both  of  which 
may  be  folded  against  the  walls  when  not  in  use,  a  chair,  a  telephone, 
and,  in  certain  classes  of  experiments,  with  a  bicycle  ergometer.  A 
view  of  the  interior  taken  from  the  window  is  shown  in  figure  7,  and 
in  figure  8  a  cross-section  of  the  chamber  showing  the  location  of  some 


To  face  page  12. 


FIG.  7. — Interior  of  Respiration  Chamber.  Bicycle  Ergometer  in  Foreground.  Food  Aperture  with 
door  open  in  rear.  Heat-Absorbing  System  and  Aluminum  Troughs  near  Ceiling.  Electrical- 
Resistance  Thermometer-Coil  just  above  Food  Aperture. 


f 
THE   RESPIRATION   APPARATUS.  13 

of  the  furniture  and  fixtures  is  given,  while  figure  33,  on  page  124,  gives 
a  clearer  presentation  of  the  interior  appearance. 

The  ceiling,  floor,  and  walls  of  the  chamber,  with  the  exception  of 
the  window  and  the  various  other  small  openings  to  be  described,  are 
constructed  of  sheet  copper.  The  use  of  metal  is  especially  advanta- 
geous in  securing  an  airtight  chamber.  A  so-called  "  i4-ounce  "  sheet 
copper  (Brown  &  Sharpe  gage  No.  24),  cold-rolled,  was  selected,  extra 
large  sheets  being  specially  obtained  to  reduce  the  number  of  seams  to 
a  minimum.  For  the  floor  of  the  chamber  two  of  the  sheets  were 
soldered  together  in  such  a  manner  that  one  seam  runs  lengthwise  of 
the  chamber,  and  were  then  cut  to  the  area  and  form  of  the  chamber 
(the  corners  being  rounded,  as  shown  in  several  of  the  figures  given). 
The  ceiling  is  a  duplicate  of  the  floor.  For  the  sides  and  ends  of  the 
chamber,  five  of  the  sheets  were  soldered  together  side  to  side,  and  bent 
to  conform  with  the  ceiling  and  floor,  which  were  then  soldered  to  the 
upper  and  lower  edges. 

The  copper  chamber  thus  constructed  is  fastened  to  a  wooden  frame- 
work or  skeleton  by  means  of  strips  of  copper  soldered  to  the  outside  of 
the  chamber.  Beneath  the  copper  floor  the  framework  is  made  solid — 
practically  a  wooden  floor — to  prevent  the  denting  and  puncturing  of  the 
copper  when  stepped  upon. 

The  respiration  chamber  also  serves  as  a  calorimeter  chamber  and  is 
fitted  with  many  devices  for  the  maintenance  of  constant  temperature. 
For  this  purpose  the  chamber  just  described  is  surrounded  by  a  similar 
chamber  of  zinc  and  an  outer  casing  of  wood.  Detailed  description  of 
these  features  is  deferred  to  that  portion  of  the  report  dealing  with  the 
calorimetric  apparatus. 

OPENINGS  IN  THE  CHAMBER. 

While  the  copper  wall  of  the  chamber  is  carefully  soldered  at  all 
joints,  and  therefore  perfectly  airtight,  it  contains,  as  has  been  indi- 
cated, a  number  of  special  openings.  Certain  precautions  are  neces- 
sary at  these  points  to  guard  against  leakage  of  air  into  or  out  of  the 
system. 

Window. — The  largest  opening  is  that  which  serves  both  as  door  and 
window,  shown  at  the  front  end  of  the  chamber  in  figures  3  and  8.  It 
is  49  cm.  wide  and  70  cm.  high,  being  of  sufficient  size  to  allow  a  man 
to  enter  comfortably  and  to  introduce  and  remove  the  various  pieces  of 
apparatus.  A  strip  of  metal  which  forms  a  small  shoulder  or  beading 
on  the  inside  of  the  window  frame  is  securely  soldered  on  all  four  sides. 
The  opening  itself  is  finally  closed  by  a  piece  of  plate  glass  which  rests 


14  A   RESPIRATION   CALORIMETER. 

against  the  metal  shoulder  and  is  held  in  place  and  made  airtight  by 
being  thoroughly  cemented  with  a  wax  prepared  by  melting  together  9 
parts  of  beeswax  and  2  parts  of  Venice  turpentine.  The  wax  is  first 
crowded  around  in  the  space  between  the  edge  of  the  glass  and  the 
metal,  and  then  by  means  of  a  soldering  iron  it  is  melted  and  pressed 
into  every  crevice.  A  pin-hole  through  the  wax  is  disastrous  to  accu- 
rate work.  As  the  result  of  a  number  of  tests,  we  have  found  that  this 
method  of  closing  the  window  is  very  satisfactory. 

Food  aperture. — For  passing  smaller  objects,  e.g.,  food  containers, 
etc. ,  into  and  out  of  the  respiration  chamber  during  the  progress  of 
an  experiment,  it  is  necessary  to  provide  an  opening  which  can  be 
opened  and  closed  without  leakage  of  air.  The  arrangement  adopted 
consists  practically  of  a  brass  tube  through  the  walls,  with  a  hinged 
port  at  each  end,  such  as  is  used  on  vessels.  (Figs.  8  and  33.) 

The  inner  port  is  soldered  directly  to  the  copper  wall  and  to  a  metal 
ring  which  in  turn  is  soldered  between  the  zinc  and  the  copper  wall. 
The  door  closes  on  a  rubber  gasket  making  an  airtight  joint.  The 
outer  port  is  tightly  soldered  to  a  brass  tube  24.3  cm.  long  and  15.2  cm. 
in  diameter,  which  extends  into  the  food  aperture  to  within  5  mm.  of 
the  door  on  the  inside.  This  brass  tube  has  a  smaller  diameter  than 
that  of  the  metal  tube  soldered  between  the  metal  walls,  and  there  is 
accordingly  an  annular  space  between  these  metal  tubes.  Since  the 
inside  port  is  soldered  to  the  ring  forming  the  outer  boundary  of  this 
annular  space  and  the  outside  port  is  soldered  to  the  tube  forming  the 
inner  boundary,  it  is  only  necessary  to  fill  this  space  completely  to  make 
an  airtight  joint.  After  considerable  experimenting  with  solid-rubber 
rings,  cement,  wax,  etc.,  a  flat  rubber  tube  with  a  smaller  tube  and 
valve  attached  to  it  in  such  a  manner  that  it  could  be  inflated  like  a 
bicycle  tire  was  utilized.  (See  D,  fig.  8.) 

The  smaller  tube  and  valve  project  through  the  outer  wall  of  the 
calorimeter  just  below  the  opening  for  the  food  aperture.  The  large 
rubber  tube  is  held  in  place  between  the  two  metal  tubes  by  a  thick 
coating  of  shellac,  and  when  once  put  in  place  and  well  inflated  a  tight 
closure  is  maintained. 

Air-pipe  openings. — The  openings  for  the  pipes  conducting  the  air 
into  and  out  of  the  chamber  are  placed  on  the  right  of  the  front  end 
of  the  chamber  (see  V,  figs.  8  and  30)  a  little  above  the  center  line. 
The  two  round  openings  in  a  rectangular  box  (see  fig.  30)  are  the  air- 
pipe  connections.  The  construction  of  the  box,  the  connection  of  the 
pipes,  and  the  method  of  attaching  and  securing  tight  closure  to  the 
copper  wall  are  shown  in  detail  in  figures  32  and  33.  Two  heavy  brass 
flanges,  threaded  on  the  inside,  are  well  soldered  to  the  copper  wall,  the 


THE   RESPIRATION   APPARATUS. 


S.    3 


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1 6  A   RESPIRATION   CALORIMETER. 

one  about  96  mm.  above  the  other.  Two  brass  pipes,  40  mm.  internal 
diameter,  1 70  mm.  long,  are  screwed  into  these  shoulders.  To  provide 
for  slight  differences  in  the  exact  position  of  the  chamber  when  it  is 
withdrawn  and  again  put  in  place  in  the  wooden  house,  it  was  found 
desirable  to  have  the  final  coupling  with  the  outside  air-pipes  more  or 
less  flexible,  and  consequently  the  coupling  was  attached  to  the  brass 
pipes  screwed  into  the  wall  by  short  lengths  of  thick- walled  rubber 
tubing.  A  small  wooden  box  with  openings  for  the  two  pipes  was 
attached  by  wax  and  small  nails  to  the  zinc  wall  of  the  chamber  and 
wooden  upright  between  the  zinc  and  copper  walls.  The  box  was  so 
adjusted  that  it  held  the  flexible  couplings  in  the  proper  position  for 
satisfactory  connection  to  the  outer  air-pipes.  Plaster  of  Paris  was 
poured  into  the  top  of  the  box  and  the  whole  mass  allowed  to  set ; 
this  serves  as  an  excellent  support  for  the  pipes,  and  yet  the  flexibility 
of  the  rubber  allows  considerable  twisting  motion  in  making  the 
connections.  When  the  chamber  is  put  in  place  in  the  house  the 
rectangular  box  supporting  the  air-pipes  fits  perfectly  into  an  opening 
through  the  two  front  panels,  shown  to  the  left  of  the  window  open- 
ing in  figure  31.  The  box  is  sufficiently  long  to  project  clear  through 
both  wooden  walls  and  thus  allow  the  making  of  an  easy  connection 
with  the  air-pipes  outside.  With  this  arrangement  there  can  be  no 
leakage  through  the  air-pipes  or  through  the  joint  between  the  air-pipe 
and  the  inner  copper  wall. 

Opening  for  weighing  apparatus. — In  order  to  permit  of  accurate 
weighing  of  the  subject  inside  the  respiration  chamber,  the  weighing 
apparatus  shown  in  figure  46  is  situated  on  the  floor  of  the  room 
above  the  chamber  and  a  metal  rod  connects  the  scales  with  the  chair 
upon  which  the  subject  sits ;  consequently  an  opening  through  the 
top  of  the  chamber  is  necessary  to  allow  the  passage  of  this  rod.  This 
opening  is  35  mm.  in  diameter,  and  consists  of  a  hard  rubber  tube 
tightly  screwed  into  a  metal  flange  soldered  to  the  top  of  the  copper 
wall.  When  the  weighing  apparatus  is  not  in  actual  use  the  opening 
is  closed  by  a  tightly  fitting  rubber  stopper.  A  number  of  tests  have 
shown  that  this  closure  can  be  made  uniformly  without  leak. 

Opening  for  the  water-pipes. — As  is  described  in  detail  beyond,  a  water 
current  is  used  to  bring  away  the  heat  generated  by  the  subject.  The 
passage  of  this  current  through  the  metal  walls  was  secured  by  solder- 
ing to  the  opening  in  the  walls  a  stiff  metal  ring,  as  in  the  case  of  the 
food  aperture.  A  round  wooden  plug,  previously  well  boiled  with  par- 
affin to  render  it  non-porous  and  so  prevent  gain  or  loss  of  water,  was 
then  driven  firmly  into  this  ring  and  tightly  sealed  by  means  of  wax. 
The  plug  is  shown  in  position  in  figure  30  immediately  at  the  right  and 


t 

THE   RESPIRATION   APPARATUS.  1 7 

a  little  below  the  window  opening,  and  also  in  figure  32.  The  water- 
pipes  were  embedded  in  this  plug,  side  by  side,  about  55  mm.  apart, 
and  the  orifice  sealed  with  wax  at  the  point  where  the  pipes  leave  the 
plug  inside  the  chamber.  By  this  means  it  is  possible  to  have  the 
water  current  enter  and  leave  the  chamber  without  leakage  of  water  or 
air.  Through  the  wooden  plug  also  pass  two  wires  used  in  the  meas- 
urement of  the  temperature  of  the  incoming  air  current  (p.  122).  The 
openings  through  which  these  wires  pass  are  likewise  sealed  with  wax. 

Rod  for  adjusting  position  of  shields. — In  order  to  raise  and  lower  the 
aluminum  shields  of  the  heat-absorbing  system  described  beyond,  a 
rod  passes  through  the  metal  walls  and  connects  on  the  outside  with  a 
lever  handle  shown  immediately  beneath  the  window  in  figure  2,  and 
with  a  metal  quadrant  (see  fig.  32)  to  which  the  phosphor-bronze  cables 
leading  to  the  shields  are  attached  on  the  inside  of  the  chamber.  In 
order  to  make  the  closure  through  which  this  rod  passes  airtight,  we 
rely  on  a  long  close  telescope-fit  between  the  outside  of  the  steel  rod 
and  the  inner  wall  of  the  brass  tube,  which  is  soldered  between  the  two 
metal  walls.  As  an  additional  precaution,  two  or  three  layers  of  cotton 
wicking,  well  soaked  with  vaseline,  are  wound  around  the  steel  rod 
next  the  copper  wall,  the  pressure  of  the  lever  handle  on  the  outside 
holding  the  wicking  tightly  in  place. 

Electric-cable  tube. — The  various  electric  circuits  used  in  temperature 
measurements  and  for  the  telephone  are  brought  together  to  form  a  large 
cable  which  passes  through  an  opening  in  the  two  metal  walls,  shown 
in  figure  29,  a  little  above  the  center  of  the  side  of  the  chamber.  In 
this  opening,  as  in  the  food  aperture  and  wooden  plug,  a  copper  tube 
was  soldered  to  both  the  zinc  and  the  copper  walls.  The  cable  was 
then  inserted  and  the  absolute  closure  made  by  coating  the  space  be- 
tween the  cable  and  both  the  inside  and  the  outside  ends  of  the  copper 
tube  between  the  two  walls  with  wax.  Furthermore,  to  prevent  a  leak- 
age of  air  through  the  cable  itself  (between  the  strands) ,  wax  was  melted 
into  the  end  of  the  cable  at  the  point  where  the  wires  separate. 

PIPING  AND  VALVES  TO  THE  BLOWER. 

The  air  from  the  chamber  passes  through  the  opening  A2  (fig.  33) 
to  the  air-pipe  leading  to  the  blower.  This  pipe  is  of  galvanized  iron 
25  mm.  in  diameter,  with  ordinary  steam  fittings  and  connections.  After 
the  piping  had  been  put  in  place  it  was  subjected  to  a  test  of  50  pounds 
pressure  to  the  square  inch. 

The  air  leaves  the  chamber,  rises  through  a  short  length  of  pipe, 
and  then  passes  along  the  ceiling,  makes  a  turn  at  the  corner  of  the 


1 8  A   RESPIRATION   CALORIMETER. 

chamber,  and  descends  into  the  blower.  The  passage  of  75  liters  of 
air  through  this  size  and  length  of  pipe  results  in  a  slightly  diminished 
pressure  (3  cm.  of  water). 

From  time  to  time  a  sample  of  air  is  withdrawn  from  this  pipe  for 
analysis,  it  being  assumed  that  the  composition  of  the  air  in  the  pipe 
between  the  chamber  and  blower  is  essentially  that  of  the  air  in  the 
chamber.  (See  p.  81.)  To  obtain  a  valve  that  will  close  completely, 
an  opening  in  the  pipe  in  which  there  is  a  diminished  pressure  has  been 
found  a  difficult  thing,  and  recourse  was  had  to  a  mercury  valve  which 
was  attached  to  the  vertical  section  of  the  pipe  above  the  blower.  This 
valve  consists  of  a  glass  Y  tube,  one  arm  of  which  was  attached  to  the 
air-pipe  and  the  other  connected  to  the  residual-analysis  apparatus. 
To  the  stem  of  the  Y  a  glass  bulb  filled  with  mercury  was  attached  by 
means  of  a  piece  of  rubber  tubing.  By  raising  this  bulb,  mercury  rises 
in  the  stem  of  the  Y  tube  and  closes  the  connection  between  the  two 
arms  of  the  Y.  On  lowering  the  valve  a  free  passage  is  obtained  for 
the  air. 

An  ordinary  one-inch  ' '  angle ' '  valve  was  placed  in  the  pipe  as  it 
descends  from  the  ceiling  to  aid  in  testing  the  air-circuit  from  time  to 
time.  This  valve,  as  well  as  that  in  the  return  air-pipe,  is  shown  in 
figure  5,  near  the  ceiling. 

THE   ROTARY   BLOWER. 

Considerable  difficulty  has  been  experienced  in  obtaining  a  suitable 
apparatus  for  maintaining  the  ventilating  current  of  air  in  the  system. 
An  attempt  was  made  to  use  the  Blakeslee  mercury  pump  used  in  the 
earlier  type  of  respiration  apparatus,1  but  the  possible  danger  of  mer- 
cury vapor  in  the  air  prevented  its  use  in  a  closed  circuit.  Several 
other  forms  of  mechanical  pumps  were  devised,  built,  and  tested,  but 
were  ultimately  discarded  in  favor  of  a  rotary  blower.  A  blower  was 
obtained  in  the  market,  and  after  undergoing  modification  was  adapted 
to  the  specific  purpose  of  maintaining  a  ventilating  current  of  air  for 
this  apparatus.  The  advantages  of  a  rotary  blower  over  a  pump  are 
numerous.  In  the  first  place,  the  current  of  air  is  very  much  more 
constant,  since  with  the  pump  there  is  more  or  less  intermittent  motion  ; 
but  more  important  than  any  other  is  the  fact  that  it  is  possible  to 
immerse  the  rotary  blower  in  oil  and  thus  minimize  and  detect  leakage 
of  air. 

The  blower  and  the  receptacle  containing  cylinder  oil  in  which  the 
blower  is  immersed,  together  with  the  air-pipes  leading  to  and  from 
the  blower,  are  shown  in  figure  9. 

1U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63,  p.  31. 


THE    RESPIRATION   APPARATUS. 


The  blower  consists  of  a  cylinder  A,  perforated  laterally  by  the  open- 
ings a  and  b  for  the  entrance  and  exit  of  the  air  current.  Inside 
the  cylinder  and  arranged  eccentrically  with  it  is  a  revolving  drum  B, 
bearing  on  its  axis  the  rod  F  which  carries  at  each  end  a  piston, 
G  and  G1.  The  piston  G  has  a  tight  connection  with  the  rod,  while 
G1  is  cushioned  on  the  springs  H.  As  the  drum  B  is  revolved  the  rod 
slides  so  that  the  pistons  press  against  the  inner  face  of  the  cylinder 
and  prevent  a  backward  escape  of  air,  and  the  current  entering  through 
a  is  forced  out  through  b  into  the  absorber  system. 

The  box  in  which  the  blower  is  placed  is  made  of  cast  iron  and  provided 
with  stuffing-boxes  through  which  the  shaft  or  axis  of  the  revolving 
drum  B  and  the  pipes  a  and  b 
pass.  Any  leakage  of  air  in 
the  blower  is  instantly  detected 
by  the  bubbles  of  air  in  the 
thick  cylinder  oil.  The  shaft 
is  oiled  by  unscrewing  two  long 
rods,  which  are  tapped  into 
oil-holes  on  each  side  of  the 
blower.  Leather  washers  on 
the  rods  insure  tightness  when 
screwed  down.  To  avoid  es- 
cape of  air  the  blower  is  oiled 
only  when  at  rest. 

In   order  that   no   oil  may 

be  drawn  into  the  absorbing  FIG.  9.— Rotary  Blower.  Air  enters  at  a,  is  forced  about 
System  a  trap  is  provided,  as  ^e  Drum  B  by  Sliding  Pistons  G  and  Oi,  and  is  driven 

shown  in  figure  10.     The  tube 

.t  is  prolonged  into  the  blind  passage  s  s.  The  oil  collects  in  the  bottom 
of  this  tube,  and  by  removing  the  plug  h  may  be  drawn  off  from  time 
to  time.  It  is  impossible  to  eliminate  the  use  of  a  small  amount  of 
lubricating  oil  from  a  blower  of  this  type,  but  we  have  found  that  the 
amount  of  oil  mechanically  carried  forward  by  the  air  current  is  ex- 
tremely small  and  is  practically  all  collected  in  the  trap.  Furthermore, 
before  reentering  the  chamber  the  air  passes  through  strong  sulphuric 
acid,  by  which  any  hydrocarbons  would  be  absorbed.  On  the  other 
hand,  the  partial  reduction  of  sulphuric  acid  to  sulphurous  acid  as  a 
result  of  the  absorption  of  hydrocarbons  would  do  little  harm,  because 
of  the  absorption  of  this  gas  by  the  soda  lime. 

The  efficiency  of  the  blower  was  tested  by  connecting  it  with  a  gas- 
meter  for  several  weeks.  It  was  found  that  the  amount  of  air  forced 
through  the  meter  was  almost  directly  proportional  to  the  speed  of 


20  A   RESPIRATION   CALORIMETER. 

the  blower  ;  consequently  the  meter  was  deemed  unnecessary  and  was 
removed. 

For  simplicity  and  efficiency,  it  is  very  much  to  be  doubted  if  an 
apparatus  could  be  devised  which  would  materially  improve  the  condi- 
tions now  obtained  with  this  simple  form  of  blower.  While  the  pressure 
of  the  air  is,  under  the  conditions  here  used,  but  35  mm.  of  mercury, 
tests  have  shown  that  the  blower  would  give  still  greater  pressures  in 
case  they  were  necessary. 

By  means  of  a  small  counter-shaft  attached  to  the  ceiling  of  the  calo- 
rimeter laboratory,  it  is  possible  to  start  and  stop  the  blower  without 
disturbing  the  other  machinery. 

MERCURY  VALVES. 

Inasmuch  as  the  experimental  day  is  generally  subdivided  into 
twelve  periods  of  two  hours  each,  it  is  necessary  to  provide  means  for 
diverting  the  main  air  current  at  the  end  of  each  experimental  period 
through  a  second  series  of  absorbers,  and  thus  provide  for  the  weighing 
of  the  water  and  carbon  dioxide  absorbed  by  the  first  set.  Accordingly, 
the  main  air-pipe  conducting  the  air  from  the  blower  to  the  absorbers 
and  that  leading  from  the  absorber  system  to  the  respiration  chamber 
are  divided,  and  a  system  of  valves  is  employed  to  cut  off  the  air-circuit 
at  the  beginning  and  end  of  each  of  the  absorber  systems.  The  two 
valves  at  the  end  nearest  the  blower  are  shown  in  figure  3,  and  figure 
4  shows  the  two  valves  at  the  opposite  end.  A  closer  view  of  these 
valves  is  given  in  figure  18.  By  opening  the  valve  at  each  end  of  one 
set  of  absorbers  and  closing  both  corresponding  valves  on  the  other  set, 
air  can  be  caused  to  traverse  either  system  as  desired. 

The  requirements  for  these  valves  are  such  as  to  demand  a  special 
form  of  construction.  At  the  point  where  the  air  enters  the  absorbing 
system  it  is  under  an  increased  pressure  of  40  to  50  mm.  of  mercury. 
At  the  other  end,  i.  e.,  where  the  air  leaves  the  absorbing  system,  it  is 
at  atmospheric  pressure.  While  the  problem  of  a  valve  at  the  exit  end 
of  the  system  is  simple,  that  of  devising  a  suitable  one  for  the  other 
end  presented  certain  difficulties  which  were  overcome  only  after  consid- 
erable time.  It  is  necessary  that  this  valve  should  be  sufficiently  tight 
to  withstand  without  a  leak  an  increased  pressure  of  40  to  50  mm.  of 
mercury  while  the  ventilating  current  of  air  is  passing  through  it.  On 
the  other  hand,  for  a  period  of  at  least  two  hours  the  valve  must  be  capa- 
ble of  being  closed  absolutely  with  atmospheric  pressure  on  one  side  of 
the  closure  and  an  increased  pressure  of  40  mm.  of  mercury  on  the 
other.  Furthermore,  the  valve  must  be  of  sufficient  size  to  permit  the 
passage  of  75  liters  of  air  per  minute  through  it  without  a  marked 


THE   RESPIRATION  APPARATUS. 


21 


resistance.  No  valve  that  we  could  find  on  the  market  would  be  guar- 
anteed by  its  manufacturers  to  meet  these  conditions.  The  form  of 
valve  finally  used  is  shown  in  figure  10. 

The  valve  consists  of  a  mechanical  closure  which  is  subsequently 
bathed  in  mercury,  thereby  giving  a  mercury  seal.  Air  from  the 
blower  enters  the  tube  /,  passes  around  the  annular  space  s  to  the  valves, 
through  the  annular  space  a  of  the  open  valve,  up  through  the  vertical 
tube  b,  and  then  to  the  absorbers  at  d.  Figure  10  shows  the  valves  as 
in  actual  operation,  one  being  open,  the  other  closed. 


FIG.  io.— Mercury  Valves.  By  raising  the  mercury  reservoir  the  mechanical  closure  made  by  the 
valve  against  end  of  tube  b  can  be  bathed  in  mercury.  Direction  of  air  current  indicated  by 
arrows.  The  valve  at  right  is  open,  that  at  left  closed.  Tube  G  is  inserted  in  mercury  and 
is  used  for  testing  the  system. 

To  close  the  valve,  the  lower  end  of  the  tube  b  is  shut  off  mechan- 
ically by  pressing  an  iron  disk,  in  which  a  fiber  gasket  g  is  inserted, 
firmly  against  its  edges  by  means  of  the  screw  and  spindle  c.  The 
closure  is  then  made  complete  by  immersion  in  mercury.  The  glass 
reservoir  /  is  so  raised  that  mercury  can  flow  through  the  rubber  tube 
m  into  the  annular  space  a  until  the  level  desired  is  reached. 

To  prevent  leakage  of  air  along  the  spindle,  it  is  caused  to  traverse 
a  length  of  pipe,  the  lower  end  of  which  is  closed  with  a  stuffing- 
box  and  gland  nt  and  the  annular  space  between  the  spindle  and  the 


22  A    RESPIRATION   CALORIMETER. 

inner  walls  of  the  pipe  is  filled  with  mercury  which  flows  down  from 
above  through  the  small  holes  o  and  ol.  This  column  of  mercury 
is  approximately  100  mm.  long,  and  its  pressure,  increased  by  the 
50  mm.  pressure  of  the  air  current,  tends  to  force  the  mercury  against 
the  packing  at  the  bottom  and  thus  prevent  the  entrance  of  air. 
The  valve  is  constructed  of  a  2-inch  T,  which  is  galvanized  on  the 
outside  to  fill  possible  blow-holes  in  the  iron.  Before  galvanizing, 
the  ends  of  the  T  were  plugged  to  prevent  the  zinc  entering  the  inner 
part  and  subsequently  forming  an  amalgam.  A  reducer,  r,  is  fitted  in 
the  top,  and  a  short  2-inch  nipple  inserted  in  the  lower  part.  The 
lower  end  of  the  nipple  is  covered  with  a  cap,  q.  This  cap  was  made 
from  a  special  casting,  and  is  provided  with  a  small  pipe  to  which  the 
rubber  tube  m  is  attached.  The  ball  and  socket  joint  j  minimizes 
lateral  motion  and  consequent  destruction  of  the  fiber  gasket  g.  The 
pipe  b,  which  is  screwed  into  the  reducer  r,  has  its  lower  end  trued 
and  the  edges  slightly  rounded  to  prevent  cutting  the  gasket.  As  is 
seen  in  figure  10,  the  connections  from  this  pipe  to  both  the  blower 
and  the  absorbers  are  made  with  ordinary  steam  fittings.  All  the 
metal  work  of  the  valve  is  of  iron  or  steel. 

When  it  is  desired  to  open  the  valve,  the  reservoir  /  is  lowered,  and 
by  reason  of  the  pitch  of  the  under  side  of  the  cap  q  every  particle  of 
mercury  is  drained  out  of  the  valve.  The  valve  wheel  is  then  turned 
and  the  mechanical  closure  opened.  There  is  then  a  free  passage  for 
the  air  through  the  side  tube,  around  the  annular  space,  and  up  through 
the  tube  b.  When  the  valve  is  opened  the  only  chances  for  a  leak  are 
around  the  coupling  d  and  through  the  stuffing-box  n.  The  coupling 
d  is  the  same  as  is  used  at  all  other  junctions  of  the  absorbing  system, 
and  when  connected  is  always  specially  tested  (see  p.  32)  to  insure 
against  leak  at  this  point.  The  tendency  of  the  mercury  is  to  press 
out  of  the  stuffing-box  n  ;  consequently  no  leak  has  ever  been  found. 
When  the  valve  is  closed  one  of  the  chances  for  leak  is  shifted  from 
the  coupling  d  to  the  closure  of  the  pipe  b,  for  after  removal  of  the 
water-absorber  attached  at  d  the  air  in  the  annular  space  a  a  is  at  a 
pressure  of  from  30  to  50  mm.,  while  that  in  b  is  at  atmospheric  pres- 
sure. Because  of  the  mechanical  closure  on  gasket  g  and  the  mercury 
seal,  no  air  can  pass  from  a  to  b. 

It  sometimes  happens  that  the  gasket  g  becomes  worn  or  cut,  or  that 
a  particle  of  dust  gets  in  between  g  and  the  pipe  b,  thereby  preventing 
a  tight  mechanical  closure.  Under  these  conditions,  unless  the  column 
of  mercury  above  the  level  of  g  is  sufficiently  high,  there  may  be  a  slight 
leakage  of  gas  down  through  the  mercury  into  the  inside  of  tube  b. 
This  condition  is,  however,  seldom  present,  and  suitable  tests  for  such 
a  leakage  have  been  devised. 


t 

THE   RESPIRATION  APPARATUS.  23 

The  details  of  manipulation  in  changing  from  one  absorber  system 
to  the  other  are  somewhat  important.  The  first  step  is  to  open  the 
valve  at  the  exit  end  of  the  new  absorber  system.  This  operation,  of 
course,  is  not  carried  out  until  the  absorber  system  has  been  tested  and 
coupled  up,  as  described  on  page  32.  Inasmuch  as  there  is  no  tension 
in  the  pipe  leading  from  the  absorber  system  to  the  chamber,  this 
preliminary  step  does  not  affect  the  volume  of  air.  At  one-half  minute 
before  the  end  of  the  experimental  period  the  reading  of  the  pointer  on 
pan  No.  i l  is  recorded,  pan  No.  2  being  in  general  kept  empty.  At 
10  seconds  before  the  end  of  the  experimental  period  the  blower  is 
stopped.  The  mercury  reservoir  on  the  valve  connected  with  the  new 
absorber  system  is  then  lowered,  and  at  the  exact  end  of  the  experi- 
mental period  the  reading  of  the  pointer  on  pan  No.  i  is  again  recorded. 
As  soon  as  this  is  done  the  wheel  on  the  valve  connecting  with  the 
new  absorber  system  is  opened,  and  the  wheel  on  the  valve  connected 
with  the  old  absorber  system  is  simultaneously  closed.  The  mercury 
reservoir  is  then  raised  to  seal  the  closed  valve  and  the  blower  is  started. 
The  valve  at  the  rear  or  exit  end  of  the  old  absorber  system  is  still  open, 
but  inasmuch  as  the  air  is  under  no  pressure  this  valve  may  be  closed 
at  leisure. 

APPARATUS   FOR   THE   DETERMINATION   OF   WATER. 

The  water  vapor  eliminated  by  the  subject  through  the  lungs  and 
skin  is  removed  from  the  chamber  in  two  ways — part  of  it  is  condensed 
within  the  chamber  and  collected  as  drip,  but  the  major  part  is  carried 
out  in  the  air  current  as  water  vapor  and  removed  from  the  air  by 
dehydration  by  sulphuric  acid. 

COI,I,ECTION  OF  DRIP. 

Condensation  of  water  vapor  within  the  chamber  is  due  to  the  method 
of  absorbing  and  removing  the  heat  eliminated  by  the  subject,  as  ex- 
plained on  page  1 25.  The  apparatus  for  collecting  the  drip  may  be  seen 
in  figure  33,  on  page  124. 

The  temperature  of  the  water  in  the  heat-absorbing  system  is  some- 
times below  the  dew-point  of  the  air  of  the  chamber.  It  frequently 
happens,  therefore,  especially  when  the  subject  is  working  hard  and 
there  is  a  large  quantity  of  water  vapor  in  the  air,  that  the  surface  of  the 
heat  absorber  becomes  covered  with  condensed  moisture  and  the  water 
drips  from  it.  This  water  is  collected  in  the  aluminum  shields  (Sd  in 
fig-  33)  used  to  regulate  the  rate  of  heat  absorption,  which  are  pur- 
posely made  water-tight. 

1  For  a  description  of  the  pans  see  page  39. 


24  A   RESPIRATION   CALORIMETER. 

The  cold  air  which  settles  in  the  bottom  of  the  aluminum  shields 
cools  them  so  noticeably  that  frequently  they,  too,  begin  to  condense 
water  on  the  outside.  To  collect  this  water  another  trough,  or,  more 
properly  speaking,  gutter  (Dt  in  fig.  33),  is  attached  to  the  bottom  of 
each  shield  to  conduct  the  water  dripping  from  the  aluminum  trough 
to  a  proper  container  (Dc  in  fig.  33). 

The  shields  do  not  encompass  the  heat-absorber  pipes  at  the  corners, 
as  may  be  seen  in  figure  33.  It  was  frequently  found,  however,  that 
the  copper  pipe  became  coated  with  moisture  and  the  water  thus  con- 
dens  ed  dropped  to  the  floor  of  the  chamber.  To  collect  this  moisture 
the  drip-cans  into  which  the  water  from  the  troughs  is  emptied  are 
suspended  from  the  copper  pipe  at  the  corners  and  are  of  such  shape 
that  they  catch  any  water  that  drips  from  the  pipe.  The  water  may 
be  drained  from  these  cups  into  bottles  and  weighed. 

To  determine  the  total  quantity  of  water  thus  condensed  it  is  neces- 
sary to  know  how  much  remains  on  the  surface  of  the  heat  absorbers  not 
collected  as  drip.  For  this  purpose  provision  is  made  for  weighing  the 
whole  heat-absorbing  system,  as  explained  elsewhere. 

REMOVAL  OF  WATER  VAPOR  FROM  THE  AIR  CURRENT. 

The  problem  here  is  the  removal  of  a  large  amount  of  water  vapor 
from  an  air  current  flowing  at  the  rate  of  75  liters  per  minute.  For 
this  purpose  the  air  is  caused  to  pass  through  concentrated  sulphuric 
acid  in  a  specially  devised  container.  From  numerous  preliminary 
experiments  it  was  learned  that  none  of  the  common  solid  absorbents 
for  water,  such  as  calcium  chloride  and  phosphorus  pentoxide,  could 
be  relied  upon  to  remove  water  from  a  large  air  current  as  completely 
as  does  the  acid. 

DESCRIPTION  OF  THE  WATER-ABSORBERS. 

The  difficulty  with  using  sulphuric  acid  as  the  absorbent  is  that  it  is 
next  to  impossible  to  obtain  a  satisfactory  container  for  it  other  than 
glass,  and  it  was  feared  that  the  large  size  of  the  absorber  would  make 
a  glass  vessel  so  unwieldy  that  it  would  be  readily  broken.  A  large 
number  of  experiments  were  made  testing  the  resistant  powers  of  copper, 
aluminum,  hard  rubber,  gold-plated  copper,  and  various  enameled  wares. 
As  the  result  of  these  tests  it  was  found  that  enameled  iron  resisted  the 
action  of  the  strong  sulphuric  acid  admirably,  and  a  set  of  absorbers 
made  from  this  material  was  in  use  for  over  a  year.  It  was,  however, 
impracticable  to  construct  a  form  of  absorber  from  this  material  of  fewer 
than  two  parts,  and  equally  impossible  to  join  the  two  parts  so  as  to 
prevent  permanently  leakage  of  air.  Consequently  the  use  of  enameled 
ware  was  abandoned. 


t 
THE   RESPIRATION   APPARATUS.  25 

Recourse  was  then  had  to  earthenware  absorbers,  the  parts  of  which, 
by  means  of  heavy  glazing,  could  be  tightly  joined  together.  This 
type  of  absorber,  while  by  no  means  all  that  could  be  desired,  has  given 
fair  results  and  is  still  in  use.1  The  external  appearance  of  the  water 
absorber  is  shown  at  the  right  in  figure  1 1 . 

The  absorber  is  300  mm.  high,  285  mm.  in  diameter,  and  contains 
about  14.5  liters.  There  are  three  openings  in  the  top — two  40  mm. 
in  diameter  for  the  entrance  and  exit  of  the  air  current,  and  a  smaller 
one  of  15  mm.,  which  is  used  for  emptying  and  recharging  the  absorber 
with  acid.  When  the  absorber  is  in  use  this  opening  is  closed  by  a 
well-vaselined  rubber  stopper,  and  the  larger  openings  are  connected 
by  couplings  to  the  remainder  of  the  absorber  system.  For  convenience 
handles  are  put  on  each  side  of  the  absorber,  each  being  perforated  in 
the  center  to  admit  of  the  attachment  of  hooks  for  supporting  the 
absorber  during  weighing.  Each  can  is  numbered  with  enamel  paint. 

The  interior  construction  of  the  absorber  is  shown  at  the  left  in 
figure  1 1 .  The  tube  through  which  the  air  enters  extends  nearly  to 
the  bottom  of  the  can  and  has  four  openings  or  slots  in  its  lower  edge. 
A  circular  disk  not  seen  in  the  figure,  160  mm.  in  diameter,  having  a 
rim  30  mm.  deep,  with  a  large  number  of  holes  in  its  edge,  is  fastened 
30  mm.  above  the  lower  end  of  the  extension  tube.  A  larger  disk 
240  mm.  in  diameter,  having  a  still  deeper  rim  also  provided  with  holes 
in  its  periphery,  is  attached  to  the  central  tube  35  mm.  above  the  first 
disk.  Acid  is  poured  into  the  can  until  the  whole  flaring  end  of  the 
extension  tube  is  immersed  in  acid,  about  5.5  kg.  being  sufficient  for 
this  purpose.  Air  descending  through  the  entrance  tube  first  passes 
through  the  four  openings  in  the  end  of  the  tube  and,  bubbling  through 
the  acid,  collects  under  the  first  disk  ;  it  then  passes  out  through  the 
small  holes  in  the  periphery  and,  bubbling  through  sulphuric  acid  the 
second  time,  enters  the  second  chamber,  where  it  collects  under  the 
second  or  larger  disk.  It  then  passes  through  the  openings  in  the  edge 
of  the  larger  disk  and  bubbles  a  third  time  through  the  acid  to  the  sur- 
face, whence  it  escapes  through  the  second  large  opening  in  the  top  of 
the  can.  To  prevent  spattering  and  escape  of  acid  fumes  through  this 
opening  it  is  protected  by  a  perforated  earthenware  cup  filled  with  a 
layer  of  pumice  stone  and  a  layer  of  asbestos.  A  thimble  of  wire  gauze 
is  then  fitted  into  the  opening  to  prevent  any  of  this  material  from 
sifting  out  when  the  can  is  turned  over,  as  in  emptying. 

It  is  thus  seen  that  the  air  bubbles  through  acid  three  times,  and  as 
the  bubbles  are  subdivided  by  the  holes  in  the  periphery  of  the  disks,  the 

1  We  are  indebted  to  the  Charles  Graham  Chemical  Pottery  Works  of  Brooklyn, 
New  York,  for  much  assistance  in  obtaining  these  absorbers. 


26  A   RESPIRATION   CALORIMETER. 

dehydration  is  very  complete,  even  though  the  depth  of  acid  through 
which  the  air  passes  is  not  great. 

The  absorbers  are  constructed  to  withstand  increased  pressure,  and 
consequently  in  testing  for  tightness  a  water  manometer  is  attached 
and  air  forced  in.  If  a  leak  is  indicated  by  the  manometer  it  can  be 
located  by  either  coating  the  joints  with  soap  solution  or  immersing 
the  whole  absorber  in  a  vessel  of  water  and  noting  any  escape  of  air 
in  the  form  of  bubbles. 

For  connecting  the  absorbers  to  each  other  and  to  the  valve,  metal 
couplings  are  used,  but  the  desired  flexibility  of  the  parts  is  secured 
by  means  of  a  specially  made  elbow  of  rubber.1  The  simple  form  of 
coupling  shown  in  figure  n,  when  used  with  a  soft  rubber  gasket 
2  mm.  thick,  has  invariably  resulted  in  a  perfectly  tight  closure. 

Durability  of  the  water-absorbers. — When  the  absorbers  were  first 
obtained  they  gave  excellent  satisfaction  in  every  way.  After  about 
three  months'  use,  however,  it  was  noted  that  the  acid  had  penetrated  the 
earthenware  and  was  collecting  in  drops  on  the  outside  of  the  absorber. 
As  a  result  of  a  number  of  tests  it  was  found  that  after  thoroughly 
washing  the  absorbers  to  free  them  from  acid  and  then  drying  at 
1 00°  in  a  water-oven  until  thoroughly  dry,  boiling- hot  paraffin  could 
be  forced  into  the  porous  material  and  thus  prevent  leaking.  The 
hot  dry  absorber  was  removed  from  the  water-oven,  a  pint  of  boiling 
paraffin  poured  into  it  and  well  shaken  about  so  as  to  insure  contact 
with  all  portions  of  the  interior,  and  then  the  excess  of  paraffin  poured 
out.  The  openings  in  the  top  of  the  absorber  were  then  carefully 
corked  and  a  pressure  of  10  or  15  pounds  applied  by  forcing  air  into 
the  absorber  with  a  bicycle  pump.  As  the  absorber  cooled,  the  paraffin 
solidified,  filling  the  porous  portions  of  the  absorber.  This  treatment 
has  thus  far  given  excellent  satisfaction. 

Efficiency  of  the  water-absorbers. — The  greater  the  efficiency  of  the 
water-absorbers  the  fewer  required  in  series  and  the  longer  they  can  be 
used.  It  was  found  that  with  a  current  of  air  passing  at  the  rate  of  75 
liters  per  minute  an  absorber  freshly  charged  with  sulphuric  acid  would 
remove  500  grams  of  water  vapor  from  the  air  current  before  allowing 
any  water  vapor  to  pass  through  unabsorbed.  As  the  system  is  now 
arranged,  one  absorber  is  used  to  remove  the  water  from  the  air  cur- 
rent and  another  to  collect  the  water  taken  up  by  the  air  current  in 
its  passage  through  the  carbon-dioxide  absorbers.  In  practice,  a  record 
is  kept  of  the  weight  of  each  absorber,  and  when  a  gain  of  400  grams 

1  These  elbows  were  furnished  upon  specifications  by  the  Davol  Rubber  Co., 
Providence,  Rhode  Island. 


To  face  page  26. 


FIG.  it.— Water-Absorbers.  At  the  right  is  a  complete  Absorber  with  rubber  elbows  and  connections.  At  the 
left  is  represented  the  interior  of  an  Absorber,  showing  the  method  for  breaking  up  air-bubbles  as  the  air 
passes  through  the  acid,  the  device  for  preventing  the  escape  of  acid  through  outgoing  air-pipe,  and  the 
opening  by  means  of/which  the  Absorber  is  filled  and  emptied. 


FIG.  12.— A  Carbon-Dioxide  Absorber  showing  Cylinder  Cap,  Collars,  Wire-gauze  Disks,  and  Cakes  of 

spent  Soda  Lime. 


t 

THE   RESPIRATION   APPARATUS.  27 

is  noted,  /.  e. ,  100  grams  less  than  tests  have  shown  to  be  absolutely 
safe,  the  spent  acid  is  removed  and  replaced  by  a  fresh  supply. 

Supply  of  sulphuric  acid. — With  this  form  of  absorber  for  the  removal 
of  water  vapor  from  the  air  the  use  of  considerable  quantities  of  sul- 
phuric acid  is  necessary.  It  has  been  found  that  the  ordinary  grades 
of  concentrated  sulphuric  acid,  specific  gravity  1.84,  are  admirably 
adapted  for  this  work.  The  acid  is  purchased  in  carboys  and  conse- 
quently the  expense  for  this  reagent  is  small. 

APPARATUS   FOR   THE   DETERMINATION   OF   CARBON   DIOXIDE. 

As  the  air  leaves  the  first  water-absorber  it  is  perfectly  dry,  but  still 
contains  carbon  dioxide  and  is  somewhat  deficient  in  oxygen.  The  next 
step  in  the  process  of  purification  is  the  removal  of  the  carbon  dioxide. 
For  a  number  of  years  prior  to  the  introduction  of  the  closed-circuit 
system  soda  lime  of  special  preparation  was  used  in  this  laboratory 
for  removing  carbon  dioxide  from  the  air  samples  taken  for  analysis. 
The  success  attending  its  use  for  this  purpose  was  such  as  to  suggest 
it  as  a  means  for  removing  the  total  quantity  of  carbon  dioxide  from 
the  main  ventilating  air  current.  From  the  area  of  the  ordinary 
U  tube,  described  on  page  45,  the  rate  and  length  of  time  of  flow 
through  it,  and  the  length  and  weight  of  the  layer  of  soda  lime,  it  was 
calculated  that  a  soda-lime  container  with  a  diameter  of  approximately 
150  mm.  and  a  length  of  approximately  380  mm.  would  be  as  efficient 
in  removing  carbon  dioxide  from  an  air  current  with  a  rate  of  75 
liters  per  minute  (the  usual  rate  of  ventilation)  as  was  the  U  tube  in 
removing  carbon  dioxide  from  the  air  current  with  a  rate  of  2  liters 
per  minute.  After  a  number  of  experiments  an  absorber  was  devised 
which  in  its  present  form  is  shown  in  figure  1 2  and  in  cross-section  in 
figure  13. 

DESCRIPTION  OP  THE  CARBON-DIOXIDE  ABSORBERS. 

The  absorbers  are  constructed  of  seamless  drawn  brass  tubing  150 
mm.  internal  diameter,  380  mm.  long,  and  with  walls  1.5  mm.  thick. 
One  end  consists  of  a  brass  disk  to  which  a  64  mm.  length  of  brass  tube 
is  permanently  soldered  and  the  joints  stiffened  by  being  well  banked 
with  solder.  The  other  end  is  detachable  and  consists  of  a  similar  brass 
disk  somewhat  larger  in  diameter  (157  mm.),  which  can  be  drawn  up 
against  a  rubber  gasket  fitting  against  the  face  of  a  shoulder  on  the  end 
of  the  main  tube,  so  that  by  means  of  the  large  collar  C  (fig.  13)  the 
opening  can  be  tightly  closed.  All  parts  are  heavily  plated  internally 
and  externally  with  silver,  which  has  been  found  to  stand  the  action  of 
the  soda  lime  indefinitely.  For  convenience  each  can  is  lettered  with 
blue  enamel. 


28 


A   RESPIRATION    CALORIMETER. 


In  order  to  facilitate  the  passage  of  the  air  current  through  the  soda 
lime  and  prevent  channeling,  a  number  of  wire-gauze  disks  about  148 
mm.  in  diameter  and  8  mm.  in  thickness  (d,  d,  d,  in  fig.  13)  are  in- 
serted in  each  cylinder  so  as  to  divide  it  into  compartments.  In  filling 
the  cylinder  the  detachable  cover  is  removed  and  a  square  of  wire 
gauze  is  inserted  in  the  opposite  end.  A  layer  of  cotton,  dl,  about  10 
mm.  thick  is  then  inserted  and  a  cover  of  wire  gauze  is  placed  above 
it,  these  precautions  being  taken  to  prevent  any  of  the  soda  lime  from 
sifting  out.  For  the  same  reason  a  small  thimble  of  wire  gauze,  T 
(also  shown  in  the  extreme  left  of  figure  13),  is  inserted  in  each 
end  of  the  cylinder.  The  cylinder  is  then  filled  with  soda  lime  for 

about  one-fourth  of 
its  depth,  one  of  the 
wire-gauze  disks 
inserted,  a  second 
layer  of  soda  lime  of 
equal  thickness  in- 
troduced, another 

FIG.  13.— Cross-section  of  Carbon-Dioxide  Absorber.    Arrangement     ,.   .         ,,     ,  ,  .    , 

in  Cylinder,  when  Absorber  is  filled  with  Soda  Ume,  of  Wire-  dlsk  added,  a  tnird 
gauze  Disks  d,  d,  rf.  Thimbles  T,  T,  and  Square  S,  with  layer  of  layer  of  Soda  lime, 
cotton  d1.  are  here  shown. 

and  then  a  disk,  and 

finally  a  fourth  layer  of  soda  lime.  A  square  of  wire  gauze,  S,  is  then 
put  in,  the  rubber  gasket  and  cover  set  in  place,  and  the  collar  screwed 
down  tightly. 

Vise  for  tightening  absorbers . — It  is  absolutely  essential  that  this  joint 
be  tight,  and  as  it  is  not  safe  to  rely  on  the  hands  alone  for  this  closure, 
we  resort  to  the  use  of  a  clamp  and  vise  devised  by  our  mechanician, 
Mr.  S.  C.  Dinsmore,  and  shown  in  figure  14. 

This  device  consists  of  two  blocks  of  wood  which  offer  a  good  sur- 
face to  grip  the  smooth  cylinder.  By  means  of  two  metal  screws  on 
the  top  of  the  vise  the  two  jaws  are  brought  together  and  the  cylinder 
firmly  held  without  distorting  it.  A  wooden  clamp  which  is  readily 
adjustable  is  then  placed  about  the  large  collar  C  (see  fig.  13),  and  by 
means  of  this  the  end  and  the  cap  can  be  screwed  down  tightly  against 
the  rubber  gasket. 

Before  removing  the  cylinder  from  the  vise  the  tightness  of  closure 
is  tested  by  means  of  a  water  manometer  and  air-pump.  With  proper 
precautions  no  difficulty  is  experienced  in  securing  a  tight  joint.  The 
cylinders  are  weighed  on  the  large  balance  shown  in  figure  21,  being 
suspended  from  one  end  of  the  balance  beam  by  two  loops  of  wire 
fitting  over  the  small  tubes  in  both  ends  of  the  can.  When  charged 
with  soda  lime  they  weigh  approximately  from  9.3  to  9.5  kg. 


t 

THE   RESPIRATION   APPARATUS.  29 

Six  of  these  soda-lime  cans  are  always  on  the  absorber-system  table, 
three  of  them  connected  ready  for  use.  The  same  form  of  coupling, 
i.  e.,  that  shown  at  right  of  figure  13,  is  used  throughout  the  whole 
absorber  system,  i.  e.,  on  the  water-absorber  cans  and  on  the  valves 
at  both  ends  of  the  absorber  system.  The  cans  not  in  use  are  closed 
at  both  ends  with  rubber  stoppers  and  all  extra  cans  are  placed  on 
a  rack  fastened  to  the  wall.  (See  fig.  i.) 

Removal  of  spent  soda  lime  from  the  can. — After  an  absorber  has  be- 
come exhausted,  i.  e.,  when  no  further  increase  in  weight  is  observed, 
the  can  is  placed  in  the  vise  and  the  collar  started  one  or  two  turns  of 
the  thread  by  means  of  the  clamp.  The  can  is  then  carried  to  some 
convenient  place,  the  collar  unscrewed  with  the  hand,  and  the  top 
removed.  When  the  can  is  inverted  the  soda  lime  generally  slips  out 
of  the  can  without  any  difficulty.  The  spent  soda  lime  is  of  much 
lighter  color  than  the  fresh,  and  is  usually  found  to  have  agglomerated 
into  the  form  of  cakes  such  as  are  shown  at  the  right  of  figure  12.  To 
insure  the  free  removal  of  the  spent  soda  lime  the  cans  are  occasionally 
given  a  thorough  washing. 

Preparation  of  soda  lime. — The  use  of  a  partially  moist  soda  lime  for 
the  absorption  of  carbon  dioxide  seems  to  have  been  first  adopted  by 
Haldane1;  but  as  our  method  of  preparing  soda  lime  is  markedly  dif- 
ferent from  that  used  by  Haldane,  and  tests  that  we  have  made  indi- 
cate that  its  efficiency  as  an  absorbing  agent  is  considerably  greater  than 
that  of  the  earlier  preparation,  a  description  of  the  method  of  its  prepa- 
ration is  given  herewith. 

One  kilogram  of  commercial  caustic  soda,  preferably  in  the  form  of 
fine  powder,  is  dissolved  in  750  cc.  of  water  in  an  iron  dish.  We  have 
found  a  round-bottomed  iron  kettle  admirably  adapted  to  this  pur- 
pose. When  the  caustic  soda  has  all  dissolved,  or  by  stirring  with  an 
iron  poker  can  be  held  in  suspension,  and  while  the  liquid  is  still  hot 
from  the  action  of  the  soda  and  water,  one  kilogram  of  pulverized 
fresh  quicklime  is  poured  into  the  solution  with  constant  and  rapid 
stirring.  The  lime  should  all  be  added  before  the  expiration  of  10 
seconds.  The  stirring  should  be  continuous  and  the  lime  held  in  sus- 
pension as  much  as  possible.  In  a  few  seconds  the  lime  begins  to 
slack  in  the  soda  solution  and  the  mass  in  the  iron  dish  becomes  very 
hot,  large  quantities  of  steam  escaping.  Care  should  be  taken  to 
avoid  the  spattering  of  drops  of  hot  alkali.  Rubber  gloves  should  be 
worn,  and  the  operation  conducted  in  a  well-ventilated  room  or  in  the 
open  air. 

.  Physiol.  (1892),  13,  p.  422. 


30  A   RESPIRATION   CALORIMETER. 

While  the  mixture  is  cooling  the  stirring  is  continued  and  the  larger 
lumps  broken  into  smaller  bits  as  much  as  possible.  It  is  then  trans- 
ferred to  a  shallow  pan  and  broken  into  small  particles  with  a  large 
iron  pestle.  Before  being  used  the  material  is  sifted  through  wire 
gauze  with  a  mesh  4  mm.  square,  the  larger  particles  being  reduced  by 
means  of  a  pestle  to  a  size  that  will  pass  through  the  sieve. 

When  properly  made  the  soda  lime  is  sufficiently  moist  to  appear 
distinctly  damp,  no  dust  being  visible,  and  yet  not  so  damp  that  it  will 
' '  cake  ' '  when  being  crushed  with  the  pestle.  In  color  it  is  white  with 
a  slight  yellowish  tinge.  The  finished  product  is  stored  in  galvanized  - 
iron  ash-barrels  with  the  top  hermetically  sealed  by  a  tin  cover  waxed 
at  the  edges. 

The  caustic  soda  is  purchased  in  cans  varying  in  weight  from  5  to  25 
pounds,  and  as  fast  as  a  can  is  opened  it  is  emptied  into  a  large  glass 
jar,  which  can  be  tightly  closed.  The  requisite  quantity  for  each  batch 
is  weighed  out  into  a  porcelain  evaporating  dish  on  scales  weighing  to 
within  one  or  two  grams.  As  a  matter  of  fact,  the  observance  of  the 
exact  proportions  is  not  strictly  necessary,  and  probably  the  weights 
taken  vary  from  10  to  20  grams  from  those  given  above. 

The  pulverized  quicklime  is  best  obtained  by  taking  a  barrel  of  the 
best  quality  of  fresh  lime,  pulverizing  it  with  a  pestle,  and  storing  it 
in  an  iron  ash-barrel,  which  can  be  carefully  closed  at  the  top.  The 
lime  in  this  condition  is  ready  to  be  weighed  and  added  directly  to  the 
strong  lye.  It  is  important  that  the  lime  used  be  very  fresh,  and  each 
barrel  should  be  tested  to  make  sure  that  the  material  slacks  freely. 

If  the  lime  is  not  of  standard  strength,  or  if  the  proportions  of  the 
soda  and  lime  are  not  carefully  maintained,  the  mixture  is  likely  to  be 
too  moist  and  form  pasty  lumps.  In  some  instances  it  is  possible  to 
utilize  such  a  product  by  mixing  with  it  some  especially  dry  soda  lime, 
though  as  a  rule  the  product  would  better  be  rejected  and  another  lot 
of  lime  used.  With  due  precautions  and  care,  however,  the  manufact- 
ure proceeds  smoothly  and  with  minimum  waste  of  material.  A  ton 
or  more  of  this  soda  lime  has  been  made  in  this  laboratory  in  the  past 
three  years,  and  the  method  and  finished  product  have  been  all  that 
could  be  desired. 

Efficiency  of  the  carbon-dioxide  absorbers. — In  the  absorption  of  carbon 
dioxide  by  soda  lime  the  reaction  may  be  considered  as  resulting  in  the 
formation  of  calcium  carbonate  and  sodium  carbonate  from  calcium 
oxide  and  sodium  hydroxide.  Assuming  that  the  soda  lime  is  a  mix- 
ture of  equal  parts  by  weight  of  sodium  hydroxide  and  calcium  oxide, 
a  soda-lime  can  containing  6  kilos  of  soda  lime  should,  theoretically, 
absorb  not  far  from  4,000  grams  of  carbon  dioxide.  In  practice,  how- 


t 

THE   RESPIRATION   APPARATUS.  31 

ever,  the  actual  efficiency  falls  far  short  of  these  figures,  and  under  the 
most  favorable  conditions  only  about  400  grams  can  be  absorbed. 
While  this  efficiency  is  very  far  from  the  theoretical,  it  is  none  the  less 
remarkably  good,  considering  the  conditions  under  which  the  absorp- 
tion takes  place,  /.  e.,  a  solid  absorbent  limited  to  surface  absorption 
only,  and  indicates  that  the  apparatus  is  well  adapted  for  the  absorp- 
tion of  a  relatively  large  amount  of  carbon  dioxide  from  a  rapidly 
moving  current  of  air. 

The  efficiency  of  the  absorber  has  been  found  to  depend  very  largely 
upon  the  rate  of  evolution  of  carbon  dioxide.  In  the  alcohol  check 
experiments  and  in  rest  experiments  with  men,  where  the  rate  of  evo- 
lution of  carbon  dioxide  is  fairly  constant  and  does  not  exceed  50  to  60 
grams  per  hour,  the  soda  lime  is  more  completely  exhausted  than  in 
work  experiments  with  men,  where  the  amount  of  carbon  dioxide  may 
rise  to  200  grams  per  hour.  With  this  large  quantity  of  carbon  dioxide 
passing  through  the  absorber  system,  the  reaction  between  the  soda  lime 
and  the  carbon  dioxide  is  so  intense  that  the  cans  become  very  much 
heated.  The  soda  lime  seems  to  fuse  or  cake  on  the  edges,  and  the  in- 
terior of  each  section  of  soda  lime  is  thereby  partially  protected  from  the 
action  of  the  carbon  dioxide.  Under  such  conditions  it  is  found  that 
each  can  will  not,  as  a  rule,  take  up  much  more  than  from  100  to  125 
grams  of  carbon  dioxide  before  it  is  necessary  to  change.  Further- 
more, all  three  cans  in  the  system,  shown  in  figure  5,  during  a  two- 
hour  period  when  the  man  is  at  hard  work,  take  up  approximately  the 
same  amount  and  all  become  heated.  While  it  is  possible  to  use  these 
partially  exhausted  cans  during  the  night  period,  when  the  subject  is 
at  rest  and  the  rate  of  evolution  of  carbon  dioxide  at  a  minimum,  it  is 
not  found  safe  to  use  such  a  partially  exhausted  can  during  a  second 
work  period  ;  consequently  the  can  is  opened  and  the  soda  lime  re- 
moved. It  is  found  on  removing  the  different  sections  of  the  soda  lime 
that  instead  of  adhering  in  a  solid  white  cake,  as  is  the  case  when  the 
soda  lime  is  completely  exhausted  (see  fig.  12),  it  crumbles  and  falls 
apart,  except  where  the  partial  fusion  or  caking  has  taken  place.  By 
picking  out  the  larger  lumps  of  the  partially  fused  material '  the  major 
portion  of  the  unused  material  can  be  saved  and  used  to  refill  the  cans. 
In  this  way  the  efficiency  of  the  soda  lime  is  not  impaired,  and  the  total 
amount  of  carbon  dioxide  absorbed  by  a  given  weight  of  soda  lime  need 
not,  under  such  manipulation,  fall  much  below  the  maximum  amount 
under  the  most  favorable  conditions. 

*By  "partially  fused"  it  must  not  be  understood  that  the  temperature  of  the 
soda  lime  rises  to  anything  like  the  fusing  point  of  soda  lime,  but  that  there 
is  an  appearance  not  unlike  fusion. 


32.  A    RESPIRATION   CALORIMETER. 

TESTING   THE   WATER   AND   CARBON-DIOXIDE    ABSORBER  SYSTEM. 

In  a  closed-circuit  apparatus  every  precaution  must  be  taken  to  guard 
against  leakage  of  air  ;  hence  the  absorber  system  is  frequently  subjected 
to  the  most  rigid  tests  for  tightness. 

Each  water-absorber  is  tested,  immediately  after  being  weighed,  in  the 
following  manner :  A  one-holed  rubber  stopper  fitted  with  a  Y  tube  is 
inserted  in  the  coupling  of  the  water-absorber  at  the  end  through  which 
the  air  leaves  the  can.  One  arm  of  the  Y  is  connected  with  a  water 
manometer  capable  of  indicating  pressures  up  to  4  feet  of  water,  and  the 
other  arm  is  connected  by  means  of  a  length  of  rubber  tubing  to  a 
bicycle  pump  for  obtaining  an  increased  air-pressure.  A  solid-rubber 
stopper  is  used  to  insure  a  tight  closure  of  the  other  coupling  on  the 
absorber.  By  means  of  the  bicycle  pump  the  desired  pressure  is  put 
on  the  absorber,  and  the  screw  pinchcock  on  the  rubber  tube  between 
the  pump  and  the  manometer  is  then  tightly  closed.  After  a  prelim- 
inary fluctuation  in  pressure,  which  lasts  for  a  moment  or  two,  a  piece 
of  paper  is  slipped  between  the  glass  arm  of  the  manometer  and  the 
wooden  support  at  such  a  point  that  its  lower  edge  just  coincides  with 
the  bottom  of  the  meniscus.  A  leakage  of  air  from  the  absorber  is 
accompanied  by  a  fall  of  water  in  the  manometer.  No  leakage  should 
be  apparent  at  the  end  of  from  three  to  five  minutes.  At  the  conclusion 
of  the  test  the  manometer  is  disconnected  and  the  pressure  released. 

An  extended  experience  shows  that  after  the  removable  ends  of  the 
carbon-dioxide  absorbers  are  well  screwed  on  a  leak  rarely  occurs  at 
this  point ;  consequently  it  is  not  necessary  to  test  each  individual 
absorber  after  weighing. 

The  water- absorbers  are  then  coupled  with  the  three  carbon-dioxide 
absorbers  as  in  use  and  the  system  as  a  whole  is  tested  to  prove  not  only 
the  tightness  of  the  individual  absorbers  themselves,  but  also  of  all  the 
couplings.  In  this  test  a  solid-rubber  stopper  is  used  to  close  the  coup- 
lings on  the  exit  end  of  the  last  water-absorber,  and  the  Y  tube  of  the 
manometer  is  connected  with  the  side  tube  G,  figure  10,  attached  just 
beyond  the  mercury  valve.  Pressure  is  then  put  on  the  system  by 
means  of  the  bicycle  pump  and  the  tightness  of  closure  tested,  as  for  the 
separate  cans.  By  the  use  of  this  method  of  testing,  leaks  in  this  por- 
tion of  the  apparatus  have  been  practically  eliminated. 

MAINTENANCE   OP  THE   SUPPLY   OF   OXYGEN. 

To  replace  the  oxygen  consumed  by  the  subject,  as  well  as  to  main- 
tain a  constant  volume  inside  the  system,  supplies  of  oxygen  are  ad- 
mitted from  time  to  time.  The  oxygen  used  for  the  purpose  is  a  com- 
mercial product,  the  so-called  "commercial  oxygen"  manufactured  by 


FIG.  14.— Vise  for  tightening  Carbon-Dioxide  Absorbers.    Top  of  Absorber  is  held  in  a  wooden  vise 
clamp  by  two  handles  ;  Collar  held  in  special  clamp. 


FIG.  15.— An  Oxygen  Cylinder  with  Valve,  Rubber    FiG.i6.— Apparatus  for  Analysis  of  Oxygen  and  Air. 


Pressure  Bag,  and  Purifying  Attachments.  On 
opening  valve  oxygen  escapes  through  the  metal 
tube  through  the  purifying  attachments.  If  the 
pressure  is  excessive,  excess  of  gas  enters  bag. 


Two  water-jacketed  burrettes,  Bt  and  B»,  each  with 
water  reservoirs,  RI  and  Rj,  are  connected  by  the 
3-way  stopcock  C.  Pipette  H  is  connected  through 
a  capillary  (T)  with  the  apparatus. 


t 

THE   RESPIRATION   APPARATUS.  33 

the  S.  S.  White  Dental  Manufacturing  Company,  of  Philadelphia. 
This  oxygen  has  been  in  use  for  some  years  in  this  laboratory  in  con- 
nection with  the  bomb  calorimeter1  and  the  carbon  and  hydrogen 
determinations.2 

It  contains,  besides  oxygen,  from  2.5  to  8  per  cent  of  nitrogen  and 
small  quantities  of  carbon  dioxide  and  water  vapor,  but  no  appreciable 
quantities  of  hydrogen  or  gaseous  hydrocarbons.  In  preparing  it  for 
use  it  is  necessary  only  to  remove  the  carbon  dioxide  and  water  and 
determine  quantitatively  the  percentage  of  nitrogen. 

The  oxygen  is  contained  in  steel  bottles  or  cylinders  (fig.  15)  6 1  cm. 
high,  ii  cm.  in  diameter,  weighing  (exclusive  of  purifying  apparatus), 
when  charged  with  283  liters  of  oxygen  at  a  pressure  of  2,000  pounds 
to  the  square  inch,  about  7  kg. 

A  metal  yoke  is  securely  fastened  to  the  valve  with  a  screw  clamp 
and  leather  washer,  and  a  brass  T  tube  conducts  the  oxygen  into  a 
rubber  gas-bag  *  and  through  the  side  outlet  to  the  purifying  device. 
The  use  of  the  bag  is  imperative,  for  the  pressure  in  the  cylinder  is  so 
high  that  however  carefully  the  valve  is  opened  the  gas  escapes  so  sud- 
denly that  the  connections  are  liable  to  be  disturbed  unless  an  overflow 
for  the  surplus  gas  is  provided. 

The  gas  then  enters  a  large  U  tube  fastened  to  the  side  of  the  cylin- 
der by  means  of  two  rubber  bands.  The  U  tube  is  filled  with  soda 
lime,  such  as  is  used  in  the  carbon-dioxide  absorbers  in  the  main  system. 
To  prevent  any  particles  of  soda  lime  from  being  carried  mechanically 
out  of  the  U  tube,  a  tuft  of  cotton  batting  is  placed  at  the  exit  end. 
In  its  passage  through  the  soda  lime  the  gas  is  completely  freed  from 
carbon  dioxide.  It  still  retains  the  moisture  it  originally  contained, 
and  some  that  it  has  taken  from  the  moist  soda  lime.  To  remove  the 
moisture,  the  gas  is  next  passed  through  a  drying  tube  of  special  con- 
struction, filled  with  pumice  stone  drenched  with  sulphuric  acid.  A 
bulb  at  the  lower  end  allows  for  the  accumulation  of  spent  acid.  By 
an  actual  test  it  has  been  found  that  such  a  tube  will  remove  all  the 
water  vapor  from  the  oxygen  in  at  least  ten  cylinders  before  it  needs 
refilling. 

As  a  matter  of  fact,  when  the  bulb  at  the  lower  end  becomes  filled 
with  spent  acid,  the  tube  is  removed,  inclined  so  as  to  drain  out  the 

^our.  Am.  Chem.  Soc.  (1903),  25,  p.  569. 

2  Benedict,  Elementary  Organic  Analysis,  p.  4. 

3  The  bags  are  made  for  us  by  the  Davol  Rubber  Company,  of  Providence,  Rhode 
Island.     They  are  extra  heavy  wall,  of  pure  rubber,  and  will  withstand  considerable 
tension  without  noticeable  leak.     It  is  estimated  that  a  bag  21  cm.  long  (measured, 
when  folded)  will,  as  a  rule,  readily  take  care  of  2  or  3  liters  of  oxygen  without 
loss.     It  is  seldom,  however,  that  an  excessive  amount  of  gas  enters  the  bag,  as  the 
adjustment  can  usually  be  readily  made  by  means  of  the  valve. 

3B 


34  A    RESPIRATION   CALORIMETER. 

acid,  and  several  portions  of  concentrated  acid  poured  in  at  the  top, 
each  successive  portion  being  allowed  to  drain  out  before  the  next  is 
added.  Obviously  such  replenishment  of  acid  is  made  only  when  the 
purifying  system  is  to  be  changed  from  an  empty  cylinder  to  a  new 
one,  and,  as  pointed  out  above,  at  least  ten  cylinders  can  be  used  with 
each  charge  of  acid.  The  replenishment  of  the  soda  lime  in  the  U  tube 
is  made  only  when  the  reagent  becomes  exhausted,  as  is  readily  noted 
by  the  whitening  effect  on  the  reagent.  (See  p.  29.) 

By  attaching  the  purifying  device  to  the  cylinder  itself  and  noting 
the  loss  in  weight  in  the  system  as  a  whole,  the  weight  of  gas  used  can 
be  obtained,  since  it  corresponds  to  the  amount  of  oxygen  and  nitrogen 
leaving  the  cylinder.  The  quantity  of  oxygen  consumed  in  the  course 
of  24  hours  by  a  subject,  varying  as  it  does  from  350  to  1,500  liters, 
can  be  best  determined  in  this  way. 

By  means  of  the  balance  described  on  page  57  it  is  possible  to  note 
the  loss  in  weight  of  an  oxygen  cylinder  to  within  10  mg.  As  10  cc.  of 
oxygen  weigh  but  14  mg.,  it  is  thus  seen  that  283  liters  (the  contents 
of  one  cylinder)  can  be  measured  with  an  accuracy  far  beyond  that  of 
any  gas-meter  with  which  we  are  familiar.  In  all  of  the  work  with  the 
respiration  calorimeter  this  method  of  measuring  oxygen  is  constantly 
used. 

In  weighing,  the  cylinder  is  suspended  on  a  wire  from  the  balance- 
arm  by  two  loops  of  wire,  one  around  the  valve  end  of  the  cylinder  and 
the  other,  a  much  larger  loop,  around  the  bottom  of  the  cylinder.  The 
manipulation  of  the  cylinder  and  its  adjustment  on  the  balance  require 
a  little  care  on  the  part  of  the  assistant,  but  in  spite  of  the  use  of  glass 
tubes  for  absorbers  there  has  been  as  yet  no  loss  by  breakage  during 
weighing. 

ANALYSIS  OF  OXYGEN. 

Since  the  gas  in  the  cylinder  contains  nitrogen  as  well  as  oxygen, 
and  the  amount  of  oxygen  admitted  to  the  system  is  estimated  from  the 
loss  in  weight  of  the  cylinders,  it  is  obviously  necessary  to  analyze  the 
gas  and  determine  the  percentage  of  nitrogen.  As  has  been  stated,  the 
amount  of  nitrogen  generally  present  is  not  far  from  2.5  to  8  per  cent. 
There  is  also  a  small  amount  of  carbon  dioxide,  but  this  is  removed  by 
the  soda-lime  U  tube  attached  to  the  cylinder.  Of  the  three  standard 
methods  for  absorbing  oxygen,  i.  <?.,  the  use  of  potassium  pyrogallate, 
phosphorus,  and  explosion  with  hydrogen,  the  first  is  most  readily 
adapted  to  the  analysis  of  nearly  pure  oxygen.  The  method  of  analysis 
consists,  therefore,  of  measuring  a  known  volume  of  commercial  oxygen 
free  from  carbon  dioxide,  absorbing  the  oxygen  by  potassium  pyrogal- 


THE    RESPIRATION   APPARATUS.  35 

late,  and  measuring  the  residual  nitrogen.  The  form  of  apparatus  is 
shown  in  figure  16. 

The  apparatus  consists  essentially  of  two  burettes,  water- jacketed  to 
secure  more  constant  temperature,  and  connected  by  a  3-way  cock, 
which  in  turn  is  joined  to  the  regular  Hempel  gas-pipette.  The  3-way 
cock  and  glass  connections  are  made  of  capillary  glass  tubing. 

Each  fresh  cylinder  of  oxygen  is  connected  by  a  metal  yoke  from  its 
valve  with  a  T  tube,  one  arm  of  which  dips  under  a  little  water  and  the 
other  arm  of  which  is  connected  with  a  soda-lime  U  tube  and  thence  with 
the  capillary  tube  T  leading  to  the  burettes.  Before  connecting  with 
this  capillary  tube,  however,  the  oxygen  is  allowed  to  flow  for  several 
minutes  through  the  soda-lime  tube  with  just  enough  pressure  not  to 
bubble  through  the  water  of  the  escape.  The  burette  B2  and  capillary 
tube  T  have  been  previously  filled  with  water  by  opening  the  3-way 
cock  C  and  raising  the  reservoir  R2,  thus  expelling  the  air  from  the 
apparatus  into  the  room  and  leaving  the  burette  B2  and  the  tube  T 
filled  with  water.  The  stopcock  C  is  then  closed  and  the  reservoir  R2 
lowered  and  hung  at  such  a  level  that  the  water  in  the  burette  will  drop 
to  about  the  100  cc.  mark  when  the  stopcock  C  is  opened.  The  soda- 
lime  U  tube  is  connected  with  the  capillary  tube  T,  the  oxygen  mean- 
while bubbling  through  the  escape,  the  stopcock  C  slowly  opened,  and 
oxygen  drawn  into  the  burette,  the  bubbling  ceasing  or  nearly  ceasing 
while  the  burette  fills.  When  the  level  of  the  water  in  B2  is  the  same 
as  that  in  Rj  the  stopcock  C  is  closed  and  the  current  of  gas  through 
the  soda-lime  tube  stopped  by  closing  the  valve  on  the  cylinder.  After 
allowing  the  water  to  drain  down  the  side  of  the  burette  B2  for  a  definite 
length  of  time  (five  minutes),  the  reservoir  R2  is  held  immediately 
behind  the  burette  B2  in  such  a  manner  that  the  level  of  water  in  both 
is  the  same.  The  readings  of  the  volume  of  gas  in  the  burette  B2  are 
then  recorded.  By  means  of  gentle  suction  with  the  mouth  the  capil- 
lary tube  and  a  portion  of  the  rubber  tube  R  which  is  attached  to  a 
Hempel  pipette  containing  a  solution  of  potassium  pyrogallate  are  filled 
with  the  pyrogallate  solution  and  the  rubber  tube  tightly  closed  by  means 
of  a  pinchcock  P.  The  section  of  the  rubber  tube  above  the  pinch- 
cock  is  then  completely  filled  with  water  and  attached  to  the  capillary 
tube  T.  The  connection  with  the  cylinder  first  being  broken,  the 
pinchcock  is  then  opened,  slipped  on  the  glass  capillary  tube  T,  the 
stopcock  C  turned  in  such  a  manner  as  to  connect  the  burette  B.2  directly 
with  the  Hempel  pipette,  and  by  raising  the  reservoir  R2  the  oxygen  is 
transferred  to  the  pipette.  The  last  traces  of  gas  can  be  removed  from 
the  burette  and  both  capillary  tubes  by  forcing  through  them  water 


36  A    RESPIRATION   CALORIMETER. 

from  the  reservoir  R2.  When  the  last  traces  of  gas  have  left  the  capil- 
lary on  the  pipette  the  stopcock  C  and  the  pinchcock  are  closed. 

The  pipette  is  then  shaken  in  the  hand  for  five  minutes,  at  the  end 
of  which  time,  as  has  been  shown  by  repeated  tests,  the  absorption  of 
oxygen  is  complete. 

After  filling  the  upper  part  of  the  rubber  tube  R  with  water  the 
pipette  is  connected  with  the  capillary  tube  T.  On  opening  the  stop- 
cock C  in  such  a  manner  as  to  connect  the  capillary  tube  T  with  the 
burette  Bj  previously  filled  with  water,  and  by  lowering  the  reservoir  R1} 
the  unabsorbed  gas  can  be  drawn  over  into  burette  Bt.  R:  is  lowered 
sufficiently  to  cause  the  reagent  in  the  pipette  to  rise  in  the  capillary, 
completely  fill  the  rubber  tube  R  and  pass  along  the  capillary  T,  to  a 
graduation  G,  when  the  stopcock  C  is  closed.  After  waiting  about 
three  minutes  for  the  water  on  the  walls  of  burette  Bj  to  settle,  the 
reading  of  the  level  of  water  in  Bx  is  made  by  holding  the  reservoir  R, 
immediately  back  of  the  burette  in  such  a  manner  that  the  levels  in 
both  tubes  are  the  same. 

Both  burettes  B:  and  Ba  are  so  graduated  that  they  can  be  read  accu- 
rately to  o.oi  cc.  The  small  burette  El  is  graduated  from  o  to  20  cc. 
The  large  burette  B2  is  graduated  only  above  90  cc. ,  but  from  90  to 
loo  cc.  it  is  graduated  in  0.05  cc. 

In  computing  the  actual  volumes  of  gas  used  it  is  necessary  to  take 
into  consideration  the  volume  of  the  space  in  the  connection  between 
the  stopcock  C  and  the  two  burettes,  as  well  as  that  of  the  capillary 
extension-tube  T.  Before  being  used  for  gas  analyses,  both  burettes 
were  calibrated  very  accurately  by  filling  with  mercury.  It  was  thus 
found  that  to  the  reading  obtained  on  burette  B2  there  must  be  added 
a  constant  0.51  cc.  for  the  volume  of  gas  in  the  connections  between 
the  burette  proper  and  the  end  of  the  tube  T,  and  to  the  volume  as  read 
on  burette  El  there  must  be  added  a  constant  0.34  cc.  for  the  volume 
of  gas  in  the  connections  between  the  burette  proper  and  the  gradua- 
tion mark  G  on  the  capillary  tube  T. 

In  the  analyses  it  is  assumed  in  the  first  place  that  the  difference  in 
time  between  the  beginning  and  end  of  an  analysis  is  so  short  that  no 
difference  in  barometric  pressure  will  occur  that  need  be  taken  into  con- 
sideration. It  is  furthermore  assumed  that  in  general,  in  the  analysis 
of  oxygen,  the  relations  between  the  volumes  of  nitrogen  and  of  the 
oxygen  as  originally  measured  are  such  that  no  fluctuations  in  temper- 
ature ordinarily  experienced  will  affect  materially  the  percentage  of 
nitrogen  in  the  sample  of  oxygen  being  analyzed.  Consequently  the 
volume  of  gas  plus  the  correction  0.51  cc.  as  measured  on  burette  B, 
and  the  volume  of  nitrogen  as  corrected  with  the  constant  0.34  cc.  as 


THE   RESPIRATION  APPARATUS.  37 

measured  on  Bt  are  compared  directly  in  order  to  determine  the  per- 
centage. The  analyses  are  always  made  in  duplicate,  and  the  figures, 
it  is  found,  are  in  general  sufficiently  accurate  to  warrant  calculation 
to  the  second  or  even  third  decimal  place. 

It  may  be  said  of  this  apparatus  that  it  might  easily  be  made  more 
convenient  and  accurate.  Designs  for  an  improved  form  are  now  under 
consideration.  Inasmuch,  however,  as  the  apparatus  gives  excellent 
service,  it  has  not  seemed  advisable  to  delay  other  work  for  the  inev- 
itable period  of  experimentation  that  must  always  accompany  the  intro- 
duction of  a  new  form  of  apparatus.  Furthermore,  it  is  readily  seen 
that  owing  to  the  small  percentage  of  nitrogen  there  might  be  a  con- 
siderable error  in  measuring  the  absolute  volume  of  oxygen  taken  for 
a  sample  without  noticeable  effect  upon  the  final  results. 

Preparation  of  the  reagents. — Inasmuch  as  large  quantities  of  potas- 
sium pyrogallate  solution  are  used  for  the  numerous  oxygen  analyses, 
as  well  as  in  air  analyses  to  be  described  beyond,  incidental  to  a  metabol- 
ism experiment,  we  have  found  it  advisable  to  prepare  stock  solutions 
of  potassium  hydroxide  and  of  pyrogallic  acid  that  can  be  mixed  in  the 
proper  proportions  as  desired. 

The  potassium  hydroxide  solution  was  formerly  prepared  by  dissolv- 
ing 2,400  grams  of  stick  potassium  hydroxide  in  1,600  cc.  of  water. 
This  method,  however,  proved  needlessly  expensive,  and  moreover 
demanded  that  special  precautions  be  taken  to  make  sure  that  the 
"stick  potash  "  had  not  been  purified  with  alcohol,  since,  as  Hempel1 
points  out,  the  presence  of  small  quantities  of  alcohol  may  be  a  serious 
source  of  error.  It  was  found  that  a  grade  of  commercial  caustic  potash, 
sold  by  the  Roessler  &  Hasslacher  Chemical  Company,  of  New  York,  and 
costing  about  7  cents  per  pound,  could  be  substituted  to  good  advantage. 
Our  present  practice  is  to  dissolve  2,400  grams  of  this  potash  in  i  ,750  cc. 
of  water  and  filter  the  solution  when  sufficiently  cool  through  glass  wool. 

In  preparing  the  solution  of  pyrogallic  acid  100  grams  of  the  acid 
are  dissolved  in  303  cc.  of  water,  the  mixture  of  acid  and  water  being 
well  shaken  until  there  is  complete  solution. 

These  stock  solutions  are  generally  made  up  several  days  before  they 
are  needed  for  use. 

The  proportions  in  which  the  acid  solution  and  the  potassium  hydrox- 
ide solution  are  mixed  are  7  cc.  of  the  pyrogallic-acid  solution  to  44  cc. 
of  the  potassium  hydroxide  solution.  Two  sizes  of  pipettes  are  regu- 
larly used.  The  larger  pipette  requires  28  cc.  of  the  acid  and  176  cc. 
of  the  alkali  to  fill  it,  the  smaller  21  cc.  of  acid  and  132  cc.  of  alkali. 
The  acid  is  placed  in  the  pipette,  a  portion  of  the  alkali  added,  and  the 

1  Hempel,  Gas  Analysis,  1892,  p.  115. 


38  A   RESPIRATION   CALORIMETER. 

mixture  shaken.  The  remainder  of  the  potassium  hydroxide  is  then 
added,  and  after  thorough  mixing  the  reagent  is  allowed  to  cool  to  room 
temperature.  The  resultant  effect  of  mixing  the  two  solutions  and  of 
the  heat  generated  is  generally  a  slight  evolution  of  gas,  which  usually 
remains  in  the  form  of  small  bubbles  on  the  surface  of  the  reagent. 
Before  being  used  for  an  analysis  these  bubbles  are  withdrawn  by  con- 
necting a  10  cc.  pipette  with  the  rubber  tube  R,  figure  16,  and  drawing 
the  froth  into  the  pipette. 

It  has  been  found  advisable  on  mixing  up  fresh  reagent  to  shake  it 
well  and,  if  possible,  allow  it  to  stand  some  time  before  use.  The 
quantity  of  reagent  in  the  small  pipette,  i.  e.,  155  cc.,  suffices  for  five 
oxygen  analyses,  in  which  100  cc.  of  gas  are  taken  for  each  sample. 
Thus  the  absorbing  constant  of  this  reagent  is  not  far  from  2.5. 

The  usual  precautions  are  taken  to  prevent  the  deterioration  of  the 
reagent,  such  as  keeping  both  ends  of  the  pipette  closed  when  not  in 
use.  The  open  end  of  the  reservoir  on  the  pipette  is  closed  with  a 
rubber  bag. 

Converting  percentage  by  -volume  to  percentage  by  weight. — As  the 
amount  of  oxygen  and  nitrogen  admitted  from  each  cylinder  into  the 
ventilating  air  current  is  determined  by  weight  rather  than  by  volume, 
it  is  necessary  to  convert  the  percentage  composition  by  volume  to  that 
by  weight.  The  percentage  is  calculated  in  the  following  manner : 

Weight  of  i  liter  of  nitrogen  =  1.25668  grams.1 
Weight  of  i  liter  of  oxygen    =  1.42853  grams. 

Example:  In  cylinder  No.  31089  analysis  showed  5.13  percent  of 
nitrogen  by  volume. 

Grams. 

loo  liters  of  gas  contains    5.13  liters  of  N  =      6.43 
loo  liters  of  gas  contains  94.87  liters  of  O  =  135-53 

100  liters  of  gas  weighs 141.96 

6.43  H-  1.4196  =  4.541  per'cent  of  nitrogen  by  weight. 

Computation  of  percentage  of  nitrogen  by  weight  by  using  factors. — The 
percentage  of  nitrogen  in  oxygen  seldom  falls  below  2  per  cent  or 
exceeds  6  per  cent,  but  the  fluctuations  are  too  great  to  rely  on  the 
constancy  of  composition  of  a  lot  of  cylinders,  even  if  shipped  from  the 
factory  at  the  same  time  ;  consequently  it  becomes  necessary  to  analyze 
each  cylinder.  After  a  few  determinations  it  was  found  that  instead  of 
carrying  out  the  somewhat  elaborate  calculations  just  referred  to,  a  fac- 
tor could  be  used  in  calculating  directly  the  percentage  by  weight  from 
the  percentage  by  volume.  Thus,  for  all  samples  of  oxygen  containing 

1  See  page  82. 


THE    RESPIRATIO&   APPARATUS.  39 

nitrogen  in  percentages  below  2.50,  the  calculation  of  the  percentage 
composition  by  weight  can  be  very  accurately  made  by  multiplying  the 
volume  percentage  by  the  factor  0.882.  For  all  volume  percentages 
between  2.50  and  3.80  the  factor  in  use  is  0.883.  For  higher  percent- 
ages the  factor  is  increased  o.ooi  for  every  0.95  per  cent  of  increase  in 
the  nitrogen  content.  At  present  we  rely  wholly  on  this  method. 

In  order  to  minimize  the  actual  amount  of  work  during  the  progress 
of  an  experiment,  the  cylinders  of  oxygen  are  analyzed  and  the  per- 
centage composition  by  volume  and  weight  determined  several  days 
before  the  experiment  begins. 

THE   TENSION   EQUALIZERS. 

The  volume  of  the  air  inside  the  closed  circuit  is  subject  to  continued 
fluctuations  as  a  result  of  changes  in  temperature,  barometric  pressure, 
oxygen  consumption,  and  water  and  carbon-dioxide  absorption.  In 
order  to  maintain  at  all  times  atmospheric  pressure  inside  the  respiration 
apparatus,  and  thereby  reduce  to  a  minimum  the  danger  of  rupturing 
the  comparatively  thin  chamber  walls  and  the  liability  of  leakages 
throughout  the  system,  a  compensating  device  was  arranged,  which  is 
shown  in  figure  17. 

The  device  consists  of  two  pans,  connected  with  the  main  air-pipe 
and  covered  at  the  top  with  flexible  rubber  diaphragms,  which  by  their 
expansion  allow  for  considerable  variation  in  the  total  volume  of  the 
circuit.  The  diaphragms  are  made  of  pure  gum,  molded  to  fit  the  inner 
surface  of  the  pan,  and  so  formed  as  to  lap  over  the  edge.  A  stout  rub- 
ber baud  is  snapped  over  the  edge  of  the  pan  so  as  to  hold  the  edge  of 
the  rubber  diaphragm  closely  against  the  rim  of  the  pan,  making  a 
very  tight  closure.  A  hard  rubber  disk  of  a  diameter  a  few  millimeters 
less  than  that  of  the  inside  bottom  of  the  pan  is  cemented  to  the  top  of 
the  diaphragm  by  means  of  fish  glue.  Three  holes  at  equal  distance 
in  the  periphery  of  this  disk  provide  for  three  loops  of  wire  which  meet 
at  a  point  directly  above  the  center  of  the  disk  and  are  there  fastened 
to  a  small  ring.  The  weight  of  the  diaphragm  and  disk,  distributed 
as  it  is  over  the  whole  system,  exerts  comparatively  slight  pressure. 
In  order  to  eliminate  pressure  entirely,  however,  the  weight  is  counter- 
balanced by  suspending  the  diaphragm  on  a  fine,  flexible  steel  wire 
running  over  the  rim  of  a  bicycle  wheel,  the  edge  of  which  is  so  placed 
that  the  wire  hangs  perfectly  plumb  and  without  lateral  strain  or  pull. 
On  the  opposite  side  of  the  rim  of  the  wheel  a  similar  flexible  wire  is 
attached,  the  lower  end  of  which  is  weighted  with  a  counterpoise  con- 
taining shot.  The  bicycle  wheel,  having  ball  bearings,  is  extremely 
sensitive,  and  it  is  possible  to  adjust  the  weight  of  shot  in  the  counter- 


4O  A    RESPIRATION   CALORIMETER. 

poise  so  as  to  compensate  for  practically  all  the  weight  of  the  rubber 
diaphragm.  It  is  evident  that  the  higher  the  diaphragm  is  raised  the 
greater  the  proportion  of  its  weight  that  is  suspended,  as  more  of  the 
rubber  diaphragm  is  then  suspended  from  the  central  rubber  disk  and 
less  from  the  edge  of  the  pan,  though  as  a  matter  of  fact  the  slight 
variations  in  weight,  amounting  to  but  a  few  grams  for  the  different 
positions  of  the  diaphragm,  are  distributed  over  so  large  an  area  that 
it  is  impossible  to  note  any  difference  in  fluctuation  of  the  water  man- 
ometer. In  practice  the  counterpoise  is  so  adjusted  that  the  rubber 
diaphragm  remains  in  a  position  about  half  way  between  the  top  and 
the  bottom  when  all  connections  are  open. 

Under  these  conditions  it  is  assumed  that  the  pressure  on  the  whole 
respiration  system,  when  the  blower  is  not  in  operation,  is  atmospheric, 
except  in  the  carbon-dioxide  and  water  absorbers,  as  explained  on  page 
73.  The  resistance  of  the  length  of  pipe  between  the  pans  and  the 
respiration  chamber  is  sufficient  to  cause  the  pans  to  rise  rather  than 
fall  when  the  blower  is  running  and  the  pipe  is  open,  but  under  all 
conditions  of  passing  air  through  the  system  it  has  been  found  practi- 
cally impossible  to  detect  any  differences  in  pressure  in  the  chamber 
proper,  since  the  pans  so  perfectly  compensate  for  variations  in  baro- 
metric pressure  and  other  changes  in  volume. 

It  will  be  noticed  that  the  pans  are  connected  with  the  air-pipe  be- 
tween the  pump  and  the  respiration  chamber.  The  air  in  the  pans 
has  therefore  been  freed  from  carbon  dioxide  and  water.  There  is  as 
yet  no  evidence  to  indicate  that  carbon  dioxide  enters  through  the  rub- 
ber diaphragm  in  measurable  amounts.  It  has  been  found,  however, 
that  appreciable  quantities  of  water  vapor  may  be  admitted  into  the 
system  in  this  way.  To  guard  against  this  an  enameled-ware  dish, 
half  filled  with  concentrated  sulphuric  acid,  is  placed  in  the  bottom  of 
each  pan.  As  the  result  of  a  number  of  tests  it  was  found  that  when 
this  precaution  was  taken  no  weighable  quantities  of  water  vapor  enter 
the  closed  air-circuit  through  the  pans,  whatever  diffuses  through  the 
rubber  being  apparently  retained  by  the  sulphuric  acid.  To  prevent 
the  rubber  diaphragm  from  coming  into  contact  with  the  acid,  the  dish 
containing  the  latter  is  covered  with  a  wire  gauze. 

The  volume  of  air  in  each  pan  consists  of  two  portions,  one  of  which 
is  constant,  the  other  variable.  The  constant  volume  comprises  that 
portion  contained  when  the  rubber  diaphragm  is  at  its  lowest  point, 
i.  e.,  resting  on  the  gauze  cover  to  the  sulphuric-acid  dish.  The  fluc- 
tuating volume  is  limited  by  the  highest  position  of  the  diaphragm. 
The  two  pans  allow  for  fluctuations  in  volume  of  about  29  liters. 


t 
THE   RESPIRATION   APPARATUS.  41 

Calibration  of  the  pans. — In  order  to  know  accurately  the  actual  vol- 
ume of  air  in  the  system  as  a  whole,  it  is  necessary  to  take  into  con- 
sideration the  fluctuating  volume  of  air  in  the  pans,  and  consequently 
a  calibration  showing  the  volume  of  air  inclosed  by  the  rubber  dia- 
phragms at  different  positions  is  essential.  By  calculations  based  upon 
measurements  of  dimension  it  is  possible  to  determine  the  volume  of 
air  in  the  pans  when  both  diaphragms  are  down. 

By  means  of  the  valve  in  the  main  air-pipe  leading  to  the  chamber 
(see  fig.  17)  and  the  mercury  valves  at  the  exit  end  of  the  absorber 
system,  the  section  of  the  circuit  to  which  the  pans  are  attached  may 
be  sealed  off.  Furthermore,  by  means  of  a  lead  weight  attached  to  a 
hook  from  which  the  rubber  disk  is  hung,  one  of  the  pans  may  be  kept 
empty.  It  is  thus  seen  that  if  air  is  admitted  at  any  point  in  this 
portion  of  the  ventilating  air-pipe  under  these  conditions  the  rubber 
diaphragm  on  the  other  pan  will  become  inflated. 

There  is  no  condition  in  which  both  pans  need  to  be  read  when  only 
partly  filled,  and  in  practice  one  can  be  kept  either  full  or  empty.  It 
is  necessary,  therefore,  to  calibrate  completely  but  one  of  the  pans,  and 
this  has  been  done  only  with  that  shown  in  the  foreground  of  figure  17. 
It  is  sufficient  for  the  other  pan  to  determine  the  actual  amount  of  air 
contained  when  full,  and  in  order  to  facilitate  reading  and  insure  accu- 
racy it  is  customary  either  to  place  a  weight  on  the  disk  and  so  expel 
all  air  from  the  pan  or  to  attach  the  weight  to  the  outer  end  of  one  of 
the  bicycle  spokes  on  the  opposite  side  of  the  wheel  to  insure  filling. 
That  there  shall  always  be  a  rise  and  fall  through  exactly  the  same 
distance,  two  screws  are  inserted  in  the  rim  of  the  wheel  at  such  a  point 
that  when  the  pan  is  weighed  empty  a  screw  strikes  against  the  fork, 
and  thus  relieves  the  extra  weight.  Similarly,  a  screw  placed  in  the 
bicycle  rim  on  the  other  side  of  the  fork  prevents  the  weight  from 
raising  the  rubber  diaphragm  beyond  a  definite  point.  Between  these 
two  points,  therefore,  it  is  necessary  to  know  the  volume  of  air  required 
to  fill  the  diaphragm.  This  was  found  by  forcing  room  air  through 
the  Elster  meter,  then  through  sulphuric  acid  to  remove  all  moisture, 
and  finally  into  the  system  until  the  rubber  diaphragm  had  reached  its 
highest  point.  This  was  easily  detected,  for  at  the  moment  the  screw 
in  the  rim  of  the  bicycle  wheel  touches  the  fork  during  the  upward 
movement  of  the  diaphragm  an  electrical  contact  is  made,  causing  a 
bell  to  ring.  From  the  readings  of  the  meter,  including  its  temperature 
and  the  pressure  on  the  manometer,  and  the  readings  of  the  barometer 
and  thermometer,  the  volume  of  dry  air  thus  added  to  the  S3rstem  was 
readily  computed.  This  amount,  plus  the  constant  volume  of  air  con- 
tained in  the  pan  below  the  bottom  of  the  diaphragm  when  in  its  lowest 


42  A   RESPIRATION   CALORIMETER. 

position,  obviously  gave  the  entire  content  of  the  pan  when  filled.  In 
calibrating  the  other  pan  the  procedure  was  identical  with  that  outlined 
above,  save  that  the  pan  was  calibrated  for  intermediate  positions  of 
the  diaphragm .  These  were  determined  by  means  of  a  pointer  attached 
to  the  bicycle  wheel.  As  the  diaphragm  rises  or  falls  the  wheel  turns, 
and  the  pointer  travels  over  a  graduated  arc  reading  to  millimeters. 
In  the  calibration,  as  the  dial  on  the  meter  passed  each  half-liter  mark, 
the  reading  of  this  pointer  was  taken.  The  actual  volume  of  air  was 
then  determined  for  each  point  on  the  scale.  These  points  were  subse- 
quently plotted  on  a  curve,  and  as  a  result  it  is  only  necessary  to  adjust 
one  pan  so  that  it  is  either  full  or  empty,  and  to  read  the  pointer  on 
the  other  in  order  to  estimate  very  exactly,  that  is,  probably  within  o.  i 
liter,  the  actual  volume  of  air  in  the  two  pans. 

In  the  course  of  a  year's  experimenting  the  sulphuric  acid  in  the 
enamel  dishes  inside  the  pans  will  gradually  absorb  moisture  and  con- 
sequently increase  in  volume.  This  increase  in  volume  is,  however, 
negligible. 

POSSIBILITY   OF   NOXIOUS   GASES   IN   THE  SYSTEM. 

An  anticipated  objection  to  the  use  of  the  closed  circuit  was  the  pos- 
sibility of  introducing  noxious  gases  into  the  apparatus.  It  is  readily 
conceivable  that  relatively  small  amounts  of  sulphuric-acid  vapor,  or 
mercury  vapor,  for  example,  would  be  extremely  injurious  to  the  health 
of  the  subject.  Since  the  air  current  comes  in  contact  with  sulphuric 
acid  in  the  absorbers  and  to  a  less  extent  with  mercury  vapor  in  the 
valves,  it  was  especially  necessary  to  determine  carefully  the  extent  to 
which  these  substances  might  be  carried  into  the  system. 

Acid  fumes  carried  over  by  air  current. — Reference  has  already  been 
made  to  the  pumice-stone  traps  on  the  exit  tube  leading  from  the  water- 
absorbers.  These  serve  to  diminish  the  possibility  that  acid  will  be 
carried  along  mechanically.  As  an  additional  safeguard,  a  layer  of 
cotton,  kept  in  place  by  a  wire- gauze  thimble  such  as  is  used  in  the 
carbon-dioxide  absorbers,  is  inserted  in  the  rubber  tube  connecting  the 
last  water- absorber  with  the  air-pipe  leading  back  to  the  chamber.  As 
a  result  of  practical  experience  it  has  been  found  that  this  cotton  serves 
to  retain  any  acid  fumes  in  the  air  current. 

Mercury  vapor  in  the  air. — Owing  to  the  marked  susceptibility  of 
certain  individuals  to  the  toxic  properties  of  minute  quantities  of 
mercury  vapor,  care  was  necessary  to  obviate  all  danger  of  poisoning. 
As  has  been  described,  the  mercury  valve  (fig.  10)  depends  upon  mer- 
cury to  effect  a  tight  closure.  To  be  sure,  the  construction  of  this  valve 
is  such  that  when  it  is  open  and  air  is  passing  through  it  all  of  the 


t 
THE   RESPIRATION  APPARATUS.  43 

mercury  is  drained  out  of  the  valve  into  the  reservoir.  Nevertheless, 
it  is  conceivable  that  a  few  globules  might  adhere  to  the  metal  work 
and  the  mercury  gradually  find  its  way  into  the  air  current.  In  the 
first  set  of  valves,  however,  it  is  highly  probable  that  any  mercury 
vapor  passing  through  the  absorber  system  would  be  absorbed,  and 
consequently  there  remains  only  the  possibility  of  the  vaporization  of 
mercury  from  the  valves  beyond  the  absorbers. 

Since  the  volume  of  air  confined  in  the  system  is  used  over  and  over 
again,  it  might  at  first  glance  be  considered  an  ideal  place  for  the  accu- 
mulation of  mercury  vapor.  Two  circumstances  militate  against  this 
assumption.  In  the  first  place,  the  air  is  continually  being  withdrawn 
from  the  chamber,  and  any  mercury  vapor  remaining  in  it  would 
be  absorbed  along  with  the  water  in  the  water- absorbers.  Secondly, 
the  air  traverses  a  relatively  long  metal  pipe  galvanized  inside,  so  that 
the  tendency  for  amalgamation  would  be  very  great.  Likewise  the 
copper  walls  of  the  chamber  would  tend  to  retain  the  mercury.  As  a 
matter  of  fact,  in  none  of  the  experiments  thus  far  made,  in  which 
different  subjects  have  remained  in  the  chamber  for  periods  varying 
from  i  to  13  days,  have  indications  of  mercurial  poisoning  ever  been 
noted,  and  it  seems  probable  that  no  appreciable  quantity  of  mercury 
vapor  enters  the  respiration  chamber. 

Proportion  of  water  vapor  in  the  air.  — Since  the  ventilating  current 
of  air  enters  the  respiration  chamber  absolutely  dry,  the  possible  effect 
of  such  dry  air  on  the  mucous  membranes  of  the  throat  and  nose  is  of 
importance,  especially  in  long-continued  experiments.  In  the  imme- 
diate vicinity  of  the  pipe  which  conducts  the  air  into  the  chamber, 
unquestionably  the  air  is  extremely  dry.  In  the  course  of  a  very  short 
time,  however,  diffusion  produces  a  uniformity  in  the  composition  of 
the  air  in  the  chamber  which  is  probably  pretty  evenly  distributed 
throughout  the  whole  volume. 

The  total  volume  of  air  in  the  chamber  is  not  far  from  5,000  liters, 
and  if  saturated  with  water  vapor  at  20°  C.  it  would  contain  about  85 
grams  of  water  vapor.  Generally  the  amount  of  water  vapor  present 
in  the  residual  air  is  not  far  from  40  grams,  although  at  times  it  may 
be  as  low  as  25  grams.  Obviously,  then,  there  is  only  about  50  per 
cent  saturation  under  ordinary  conditions,  and  at  times  as  low  as  30 
per  cent.  This  is  not  unduly  dry  air,  and  yet  experience  has  shown 
that  it  is  capable  of  producing  certain  physical  effects  that  can  be 
attributed  only  to  excessively  dry  air.  The  subjects  very  frequently 
complain  of  being  rather  cooler  than  when  in  the  air  of  the  labora- 
tory. This  is  explained  by  the  fact  that  there  is  much  more  rapid 
vaporization  of  water  from  the  lungs  and  skin  and  consequently  a  low- 


44  A   RESPIRATION   CALORIMETER. 

ering  of  temperature.  On  one  or  two  occasions,  when  the  subject  has 
slept,  contrary  to  the  advice  of  the  experimenters,  with  his  head  near 
the  pipe  conducting  the  air  into  the  chamber,  slight  disturbances  of 
the  respiratory  tract  have  been  experienced,  but  when  sleeping  with 
the  head  at  the  other  end  of  the  chamber  no  such  disturbances  have 
occurred. 

APPARATUS   FOR  THE  ANALYSIS   OF   THE   RESIDUAL  AIR. 

For  purposes  of  calculation  it  is  necessary  to  know  the  carbon-dioxide 
and  water  content  of  the  closed  volume  of  air  at  the  end  of  each  experi- 
mental period.  While  any  one  of  the  numerous  methods  depending  on 
the  use  of  a  solution  of  barium  hydroxide  and  phenolphthalein  might 
be  used  for  the  determination  of  carbon  dioxide,  and  consequently  only 
a  very  small  volume  of  gas  required,  none  of  the  methods  of  hygrometry 
as  ordinarily  employed  will  give  the  water  content  of  the  air  with  suffi- 
cient accuracy.  It  is  therefore  necessary  to  determine  the  water  by 
the  absolute  method,  that  is,  by  aspirating  a  large  quantity  of  air 
through  some  water  absorbent  and  actually  weighing  the  water  vapor 
thus  removed.  The  arrangements  for  this  operation  are  illustrated  in 
figure  1 8. 

A  lo-liter  sample  is  withdrawn  from  the  air- pipe  between  the  respi- 
ration chamber  and  the  blower  through  the  mercury  valve  described  on 
page  1 8.  The  water  vapor  and  carbon  dioxide  are  removed  by  con- 
ducting the  sample  through  sulphuric  acid  and  soda  lime,  respectively, 
the  volume  of  air  withdrawn  being  accurately  measured  by  a  gas-meter. 
After  leaving  the  meter  the  air  enters  the  water-pump,  where  the  suc- 
tion required  to  draw  the  air  through  the  tubes  and  the  meter  is  obtained. 
A  device  for  separating  the  air  and  water  leaving  this  pump  makes  it 
possible  to  return  the  air  sample  to  the  ventilating  air  current  between 
the  pans  and  the  respiration  chamber. 

Theoretically  the  sample  of  air  should  be  drawn  at  exactly  the  end 
of  the  different  experimental  periods.  In  such  case,  however,  it  would 
necessitate  the  complete  withdrawal  of  10  liters  of  air  from  the  system 
and  introduce  serious  complications  in  the  calculations.  By  means  of 
the  system  of  U  tubes  described  beyond,  it  is  found  that  air  may  be  drawn 
through  these  tubes  at  the  rate  of  2  or  even  3  liters  in  one  minute  and 
all  the  carbon  dioxide  and  water  be  quantitatively  absorbed.  At  this 
rate  the  air  can  be  drawn  with  sufficient  rapidity  to  furnish  results  that 
agree  with  those  from  a  to-liter  sample  drawn  at  one  instant.  By 
returning  the  air  to  the  system  no  loss  occurs. 

The  requirements  for  absorbents  for  water  vapor  and  carbon  dioxide 
that  will  effect  the  complete  removal  of  these  substances  from  an  air 


TO  face  page  44. 


FIG.  17.— Pans  for  Equalizing  Pressure.  Two  painted  tin  pans  with  rubber  diaphragms  which  fit  their  interior  are 
attached  to  connecting  air-pipe.  Weight  of  diaphragms  is  equipoised  by  lead  shot  suspended  from  a  bicycle 
wheel.  Variations  in  position  of  height  of  diaphragm  are  read  on  the  graduated  arc  beneath  bicycle  wheel. 


Fio.  18.— Apparatus  for  Analysis  of  Residual  Air.  U  tubes  on  top  shelf  of  table  are  connected 
with  Klster  meter.  Glass  water-pump  and  air-separating  chamber  immediately  to  right  of 
center  posts.  Sulphuric-acid  drying  bottle  at  right  of  Elster  meter. 


RESPIRATION   APPARATUS.  45 

current  flowing  at  the  rate  of  2  to  3  liters  a  minute  are  met  by  using 
pumice  stone  drenched  with  sulphuric  acid  to  absorb  the  water  vapor 
and  the  specially  prepared  soda  lime  (see  p.  29)  to  absorb  the  carbon 
dioxide.  These  absorbents  are  held  in  glass  U  tubes. 

APPARATUS  FOR  ABSORPTION  OF  WATER. 

The  pumice  stone  is  broken  into  pieces  approximately  5  mm.  in 
diameter,  the  finer  dust  carefully  sifted  out,  and  each  arm  of  the  U 
tubes  filled  to  within  10  mm.  of  the  top.  About  10  cc.  of  commercial 
concentrated  sulphuric  acid  is  slowly  poured  over  the  pumice  stone  in 
both  arms  of  the  tube,  care  being  taken  not  to  add  so  much  acid  as  to 
completely  close  the  bend  at  the  bottom  of  the  U  and  thus  retard  the 
free  passage  of  gas.  One-hole  rubber  stoppers  provided  with  small 
glass  elbows  are  fitted  in  each  arm  of  the  U  and  a  small  label  with 
the  number  of  the  tube  is  placed  on  one  arm.  All  connections  are 
made  in  such  manner  that  the  air  leaves  the  U  tube  from  the  arm  on 
which  the  label  is  placed.  This  precaution  is  necessary,  because  as 
the  moist  air  enters  the  U  tube  the  sulphuric  acid  with  which  it  first 
comes  into  contact  takes  up  the  water  vapor  from  it,  and  consequently 
becomes  somewhat  diluted.  If  during  a  subsequent  use  of  this  tube 
the  air  were  allowed  to  enter  the  other  arm  and  pass  out  over  the 
dilute  acid  on  the  pumice  stone,  experience  has  shown  that  the  re- 
moval of  water  would  not  be  complete,  since  the  very  dry  air  would 
take  up  water  from  the  dilute  acid. 

Owing  to  the  presence  of  chlorides  in  the  pumice  stone,  the  addition 
of  sulphuric  acid  is  liable  to  produce  a  slight  evolution  of  hydrochloric- 
acid  gas,  and  consequently,  when  the  U  tubes  are  freshly  filled,  it  is 
desirable  to  draw  dry  air  through  them  for  a  few  minutes,  thus  remov- 
ing the  hydrochloric-acid  gas.  This  precaution  is  also  taken  with  the 
U  tubes  used  for  the  oxygen  purification,  described  on  page  33.  In 
this  case  it  is  of  even  greater  importance,  as  otherwise  the  hydrochloric- 
acid  gas  would  enter  the  main  air  current. 

The  U  tubes  are  130  mm.  long,  60  mm.  wide,  measured  on  the  out- 
side, and  15  mm.  in  diameter.  They  weigh,  when  fitted  with  rubber 
stoppers,  glass  elbows,  pumice  stone,  and  acid,  not  far  from  70  grams. 
When  not  in  actual  use  the  glass  elbows  are  closed  by  short  pieces  of 
rubber  tubing  fitted  with  glass  plugs. 

Efficiency  of  absorption, — It  has  been  found  by  repeated  experiment 
that  a  U  tube  filled  as  above  described  can  be  safely  relied  upon  to 
absorb  one  gram  of  water  vapor.  In  the  ordinary  usage  to  which  the 
tubes  are  subjected  in  this  laboratory,  it  is  nearly  always  possible  to 
predict  the  gain  in  weight  during  an  analysis.  Thus  if  it  is  expected 


46  A   RESPIRATION   CALORIMETER. 

that  a  tube  will  gain  in  weight  o.  1  2  gram,  it  can  have  already  increased 
in  weight  0.88  gram  with  safety.  If,  however,  the  anticipated  increase 
in  weight  will  make  a  total  gain  of  more  than  one  gram,  the  tube  is 
refilled  before  use. 

APPARATUS  FOR  CARBON-DIOXIDE  ABSORPTION. 

For  the  removal  of  carbon  dioxide,  U  tubes  similar  in  size  to  those 
used  for  water  absorption  are  employed.  Each  tube  is  filled  to  within 
10  mm.  of  the  top  with  soda  lime,  the  particles  of  which  are  not  so  fine 
as  to  obstruct  the  flow  of  gas.  The  ends  of  the  tube  are  then  closed 
with  rubber  stoppers  and  glass  elbows,  as  described  above. 

Efficiency  of  absorption.  —  In  spite  of  the  remarkable  absorptive  power 
of  soda  lime  for  carbon  dioxide,  it  is  not  advisable  to  use  a  soda-lime 
U  tube  for  more  than  one  or  two  analyses,  depending  upon  the  amount 
of  carbon  dioxide  absorbed.  As  a  rule,  it  is  not  safe  to  use  a  U  tube  in 
which  the  whitening  effect,  due  to  the  formation  of  carbonate,  extends 
more  than  half  the  length  of  the  tube. 

In  practice,  the  sample  of  air  is  drawn  through  a  sulphuric-acid 
U  tube,  a  soda-lime  U  tube,  and  a  second  sulphuric-acid  U  tube.  Any 
moisture  escaping  from  the  damp  soda  lime  is  retained  by  this  second 
sulphuric-acid  U  tube,  the  quantity  thus  absorbed  being  approximately 
i  mg.  for  every  liter  of  air  passing  through  the  soda  lime. 

THE  EWTER  METER. 


For  measuring  samples  of  air  for  residual  analysis,  a  meter  made  by 
S.  Elster,  of  Berlin,  has  been  used.  The  meter  is  shown  in  figure  18, 
just  to  the  right  of  the  U  tubes. 

This  meter  is  very  sensitive,  and  measures  volumes  up  to  10  liters,  each 
liter  being  graduated  to  2  cc.  Attached  to  it  is  a  water  manometer. 
Experiments  show  that  the  extreme  variation  in  tension  in  different 
parts  of  the  meter  when  air  is  freely  drawn  through  it  amounts  to  less 
than  5  mm.  of  water.  This  difference  holds  regardless  of  the  rate  at 
which  the  air  is  drawn  through  the  meter.  The  meter  is  provided 
with  a  spirit  level  and  leveling  screws.  The  case  of  the  meter  is  filled 
with  water,  the  excess  being  drawn  off  through  an  overflow.  Since 
the  air  enters  the  meter  dry  and  leaves  it  moist,  water  is  removed  from 
the  meter  during  the  progress  of  the  experiments.  As  used  at  present 
about  4.  5  grams  of  water  are  evaporated  during  the  course  of  24  hours  ; 
consequently  water  is  added  from  time  to  time  in  order  to  keep  a  con- 
stant level. 

In  general,  10  liters  of  air  are  drawn  for  each  residual  analysis,  the 
meter  being  read  before  drawing  the  sample  and  after  the  manometer 
has  settled  to  zero  at  the  close. 


t 

THE   RESPIRATION  APPARATUS.  47 

The  vaporization  of  water  in  the  meter  results  in  a  slight  lowering  of 
the  temperature  of  the  water  in  the  meter  as  the  air  passes  through  it. 
The  thermometer  is  read  in  the  middle  of  each  residual  sample,  i.  e. , 
when  5  liters  of  air  have  passed  through  the  meter.  This  is  assumed 
to  give  the  average  temperature  of  the  10  liters. 

Calibration  of  Elster  meter. — The  Elster  meter  was  calibrated  by  pass- 
ing a  known  weight  of  oxygen  from  a  cylinder  through  the  meter  and 
comparing  the  volume  as  calculated  from  this  weight  with  the  volume 
recorded  by  the  meter  after  making  due  corrections  in  the  latter  for 
temperature,  tension  of  aqueous  vapor,  barometer,  etc.  In  order  to 
have  the  conditions  under  which  the  gas  is  measured  correspond  as 
nearly  as  possible  to  those  under  which  residual  analyses  are  taken, 
provision  was  made  for  maintaining  during  the  test  a  diminished  pres- 
sure in  the  meter  amounting  to  198  mm.  of  water.  This  diminished 
tension  is  that  ordinarily  experienced  when  conducting  a  residual 
analysis,  and  is  a  measure  of  the  resistance  of  the  tubing,  U  tubes,  and 
meter. 

In  conducting  the  test  the  apparatus  was  connected  ready  for  use, 
the  oxygen  cylinder  weighed,  and  the  barometer  reading  taken.  At 
the  end  of  every  10  liters  the  temperature  of  the  meter  was  recorded. 
The  barometer  was  read  periodically,  but  it  was  found  that  the  fluc- 
tuations were  very  slight,  and,  in  general,  the  average  of  the  readings 
at  the  beginning  and  end  could  be  used.  After  about  100  liters  of  air 
(apparent  volume  as  measured  by  the  meter)  had  passed  through  the 
meter  the  cylinder  was  weighed  and  the  calculation  of  volume  from 
weight  was  made. 

From  a  number  of  such  tests  it  was  found  that  to  obtain  the  true 
reading  from  the  meter  under  the  conditions  of  the  experiment  the 
logarithmic  factor  .98895*  should  be  added  to  the  logarithm  of  the 
apparent  volume. 

TEST  FOR  SATURATION  OF  AIR  PASSING  THROUGH  THE  ELSTER  METER. 

In  drawing  through  the  Elster  meter  the  air  used  for  the  residual 
analyses,  it  is  assumed  that,  coming  in  contact,  as  it  does,  with  a  large 
volume  of  water  in  its  passage  through  the  meter,  it  becomes  saturated 
with  water  vapor  at  the  temperature  of  the  meter.  It  was  necessary  to 
verify  this  assumption,  especially  as  in  the  calculations  the  volume  of 
air  passing  through  the  meter  is  multiplied  by  a  large  factor  and  so 
must  be  known  with  great  accuracy.  To  test  this  point,  20. 103  liters  of 
air,  as  measured  by  the  meter,  were  forced  through  the  meter  at  a  tem- 

1  For  convenience  in  calculations  the  characteristics  of  the  logarithms  of  the 
factors  are  neglected. 


48  A   RESPIRATION   CALORIMETER. 

peratureof  17.89°  and  then  through  a  weighed  U  tube  containing  pumice 
stone  and  sulphuric  acid. 

Air  saturated  with  water  vapor  at  760  mm.  and  17.89°  contains 
0.01513'  gram  of  water  per  liter. 

In  this  test  the  air  when  passed  through  the  meter  contained  o.  3055 
gram  of  water  vapor  in  20.103  liters  apparent  volume  or  20.42  liters 
corrected  volume.  This  corresponds  to  0.3055  -^  20.42  =  0.01496  gram 
of  water  vapor  per  liter — an  agreement  inside  of  the  error  of  experi- 
mentation. It  is  assumed,  therefore,  that  the  air  passing  through  the 
meter  is  saturated  with  water  vapor. 

APPARATUS  FOR  DRAWING  SAMPLE. 

Obviously,  with  the  closed  circuit,  it  would  be  undesirable  to  remove 
from  the  system  so  large  a  sample  as  10  liters  of  air  at  the  end  of  every 
two  hours.  By  means  of  the  apparatus  shown  in  figure  19,  it  is  possi- 
ble to  draw  as  large  a  sample  of  air  as  is  desired  through  the  U  tubes, 
remove  from  it  carbon  dioxide  and  water  vapor,  and  return  it  to  the 
system  dry,  free  from  carbon  dioxide,  and  diminished  in  volume  only 
by  the  volume  of  the  carbon  dioxide  and  water  vapor  removed  by  the 
absorbents. 

The  apparatus  consists  of  a  glass  suction-pump  A,  a  separating  cham- 
ber B,  in  which  the  air  and  the  water  used  for  aspiration  are  separated, 
and  the  drying  chamber  D,  in  which  the  water  vapor  taken  up  by  the 
dry  air  from  the  water-pump  is  removed  before  the  air  is  returned  again 
to  the  system.  The  sample  of  air  after  leaving  the  U  tubes  passes 
through  the  Elster  meter  (see  fig.  18)  and  then  enters  the  suction- 
pump  at  the  tube  a.  As  the  air  and  water  issue  from  the  glass  exten- 
sion tube  they  strike  against  the  side  of  the  separating  chamber  B. 
The  water  flows  through  the  overflow  c  into  the  drain  d.  The  air 
passes  out  through  the  enlarged  tube  c,  bubbles  through  concentrated 
sulphuric  acid  in  the  drying  chamber  D,  and  finally  passes  through 
the  small  tube/  back  into  the  air  system.  It  has  been  found  by  repeated 
experiment  that  i  o  liters  of  air  saturated  with  water  vapor  at  the  tempera- 
ture of  the  laboratory,  i,  c. ,  20°,  passing  through  the  drying  chamber 
in  three  or  four  minutes,  will  be  completely  freed  from  water  vapor. 
The  acid  in  the  chamber  is  replenished  from  time  to  time  by  removing 
the  central  stopper  and  withdrawing  the  acid  by  suction. 

Two  valves,  ze>3  and  w^  are  used  to  admit  water  to  the  suction-pump. 
The  valve  w^  is  permanently  adjusted  so  that  the  supply  of  water  pass- 
ing through  the  pump  will  be  that  best  fitted  for  drawing  the  sample 

1  Smithsonian  Meteorological  Tables  (1897),  p.  133. 


THE   RESPIRATION   APPARATUS. 


49 


of  air  through  the  U 
tubes  and  meter  at  a 
proper  rate  of  flow,  while 
the  water  is  ordinarily 
turned  on  and  off  by  the 
valve  w,,.  At  t  a  glass  T 
tube  is  inserted  for  the 
rejection  of  air  (see  p. 
77),  to  the  stem  of  which 
a  rubber  tube  dipping 
into  a  small  vial  contain- 
ing water  is  attached. 
The  rubber  tube  is  ordi- 
narily closed  with  a  screw 
pinchcock,  the  tightness 
of  the  closure  being 
proved  by  the  absence  of 
bubbling  of  water  in  the 
small  vial. 

The  water  used  for  act- 
uating the  suction-pump 
enters  at  m  and  passes 
into  the  large  chamber  F, 
which  serves  as  a  trap. 
This  chamber  consists  of 
2-inch  gas-pipe  with  a  cap 
at  each  end.  To  prevent 
sediment  from  clogging 
the  fine  jet  of  the  water- 
pump,  the  supply  of 
water  for  the  pump  itself 
is  drawn  from  a  point 
somewhat  above  the  bot-v 
torn  of  the  trap.  The 
sediment  in  the  water  col- 
lects below  this  point,  and 
can  be  drawn  off  through 
the  valve  ze>2,  which  is 
always  opened  a  moment 
or  two  before  starting 
the  suction  -  pump.  To 
prevent  the  entrance  of 
air  in  the  water  current,  a 
43 


FIG.  19.— Apparatus  for  Drawing  Sample  of  Air  for  Residual 
Analysis.  A  glass  suction-pump  A  draws  air  from  the 
Elster  meter  and  delivers  it,  together  with  the  water  used 
for  aspiration,  into  separating  chamber  B.  The  water 
flows  off  through  overflow  through  pipe  d  and  the  air 
passes  through  exit  tube  t  into  drying  chamber  D. 


50  A   RESPIRATION   CALORIMETER. 

valve,  wlt  is  provided.  Any  air  that  may  have  been  brought  along  by 
the  water  current  will  accumulate  in  the  upper  part  of  the  chamber  F, 
and  when  this  valve  is  opened  will  pass  out  into  the  drain,  the  chamber 
becoming  completely  filled  with  water. 

Apparatus  for  constant  water  pressure. — In  using  a  water  suction-pump 
for  drawing  the  sample  of  air,  it  is  of  great  importance  that  the  water 
pressure  be  constant,  as  otherwise  the  air  will  be  drawn  through  the 
U  tubes  and  meter  with  a  varying  degree  of  rapidity,  and  consequently 
under  varying  tension  as  measured  by  the  water  manometer.  The 
measurement  of  the  absolute  volume  of  air  passing  through  the  meter 
is  of  great  importance,  since  its  relation  to  the  larger  volume  of  residual 
air  (10 :  5,000)  necessitates  the  use  of  a  very  large  factor  when  comput- 
ing the  residual  amounts  of  carbon  dioxide  and  water  in  the  system  ; 
consequently  every  precaution  must  be  taken  to  secure  the  most  uni- 
form sampling.  The  city  water  pressure  was  found  to  be  entirely 
inadequate  for  the  degree  of  accuracy  required  for  this  work,  and  a 
special  water  system,  shown  in  figure  20,  was  installed. 

A  force-pump,  which  is  belted  to  the  line  shaft  in  the  calorimeter 
laboratory,  draws  water  from  a  galvanized-iron  pail,  which  is  supplied 
from  the  city  main,  and  forces  it  into  an  upright  boiler,  which  serves 
as  an  air-chamber.  The  boiler  is  filled  about  half  full  of  water,  the  level 
of  which  is  noted  by  the  glass  water-gage  at  the  side,  and  then  com- 
pressed air  from  a  cylinder  is  admitted  to  the  boiler  until  the  manometer 
at  the  top  indicates  a  pressure  of  about  100  pounds.  The  water  with- 
drawn from  this  chamber  for  use  in  the  suction-pump  is  taken  from  a 
pipe  extending  several  inches  above  the  bottom  of  the  boiler,  so  as  to 
eliminate  sediment  as  much  as  possible.  By  means  of  the  valve  w±, 
figure  19,  the  supply  of  water  passing  through  the  suction-pump  may 
be  regulated  at  will. 

PROCESS  OF  TAKING  RESIDUAI,  SAMPLES. 

The  residual  analysis  is  started  at  about  10  minutes  before  the  end 
of  each  experimental  period.  Ten  liters  of  air  (apparent  volume  as 
measured  by  the  meter)  are  used  for  each  determination.  A  dupli- 
cate analysis  follows,  beginning  at  about  three  minutes  before  the  end 
of  the  experimental  period.  The  rate  of  flow  of  air  through  the  meter 
is  such  that  the  second  sample  is  about  one-half  taken  at  the  end  of 
the  experimental  period,  the  remaining  5  liters  of  air  being  taken  during 
the  beginning  of  the  next  period.  It  is  assumed  that  the  average  com- 
position of  the  sample  will  be  that  of  the  air  at  the  moment  of  changing 
from  one  period  to  another.  The  differences  in  results  by  the  two 
samples  are  usually  insignificant,  in  which  case  the  second  series  of 


THE   RESPIRATION  APPARATUS. 


results  is  invariably  used  in  the  calculations.  Occasionally,  though 
rarely,  wide  discrepancies  in  the  two  analyses  will  appear.  Under  these 
conditions  a  third  analysis  is  made  and  the  figures  agreeing  most  closely 
are  used.  In  such  cases  the  error  is  almost  always  directly  traceable. 

SAMPLING  THE  AIR   FOR  THE   DETERMINATION   OF   OXYGEN. 

Of  the  four  constituents  of  the  ventilating  current  of  air,  carbon 
dioxide,  water  vapor,  nitrogen,  and  oxygen,  the  amounts  of  the  first 
two  in  the  residual  air  are  determined  by  the  apparatus  described 
above.  In  order  to  know  accurately  the 
amount  of  oxygen  in  the  air,  a  determina- 
tion of  this  element  is  necessary. 

The  actual  determination  of  oxygen  in 
the  air  current,  by  absorption  by  potassium 
pyrogallate,  is  usually  made  once  each  24 
hours,  the  sample  being  generally  drawn  at 
the  close  of  the  experimental  period  ending 
at  7  a.  m. 

It  is  of  great  im- 
portance to  obtain 
a  sample  of  air  in 
which  the  percent- 
age of  oxygen  shall 
represent  accurately 
that  in  the  respira-. 
tion  chamber.  For- 
merly the  air  was 
sampled  after  it  had 
passed  through  the 
blower  and  absorb- 
ing system,  and  it 
was  assumed  to  be 


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FIG.  20.— Water-Pressure  System.  Water  from  reservoir  at  left  is  forced  by  pump  into  the  large 
air-tank  at  right.  The  release  valve  immediately  to  right  of  pump  returns  the  water  to  reservoir 
in  case  pressure  in  tank  exceeds  100  pounds.  Water  is  drawn  from  tank  for  suction-pump  used 
for  drawing  residual  samples. 


52  A   RESPIRATION   CALORIMETER. 

free  from  carbon  dioxide  when  taken  under  these  conditions.  It  was 
found,  however,  that  at  the  time  when  the  air  sample  is  usually  taken, 
i.  e.,  immediately  after  the  end  of  the  experimental  period,  the  air  in  the 
main  ventilating  pipe  leaving  the  absorbers  is  a  mixture  of  purified 
air  from  the  respiration  chamber  and  normal  air  from  the  laboratory 
contained  in  the  carbon-dioxide  and  water  absorbers  that  had  just 
been  put  into  use,  and,  since  the  percentage  of  oxygen  in  the  normal 
air  is  somewhat  larger  than  that  in  the  air  from  the  chamber,  the  pro- 
portion of  oxygen  in  the  sample  would  of  course  be  too  large.  If  the 
taking  of  the  sample  was  delayed  for  several  minutes,  i.  c, ,  until  the 
air  in  the  absorbing  system  had  been  thoroughly  swept  out,  this  diffi- 
culty was  no  longer  experienced,  but,  as  any  delay  in  taking  the  sample 
of  air  was  accompanied  by  a  gradually  varying  percentage  of  oxygen,  it 
was  evident  that  this  method  of  taking  the  sample  was  erroneous.  To 
avoid  these  difficulties,  the  air  that  has  been  through  the  residual  U  tubes 
and  meter  is  now  utilized  as  the  sample.  Inasmuch  as  this  sample  is 
always  taken  during  the  second  residual,  i.  e. ,  after  the  air  in  the  meter 
has  been  thoroughly  swept  out  by  air  of  the  same  composition  as  the 
sample,  the  air  thus  collected  probably  represents  better  than  any  other 
the  true  composition  of  the  carbon-dioxide  free  air  inside  the  chamber. 

METHOD  OF  SAMPLING. 

It  has  been  found  that  if  the  analyses  are  made  immediately  after 
drawing  the  sample  the  air  may  be  collected  in  an  ordinary  rubber 
foot-ball  bladder.  In  taking  the  sample  it  is  customary  to  slip  the 
rubber  neck  of  the  bag  over  the  glass  tube  connecting  with  the  T  tube 
(/,  fig.  19).  The  rubber  neck  of  the  bag  is  provided  with  a  screw 
pinchcock.  On  opening  this  pinchcock  and  the  one  above,  air  rushes 
into  the  bladder  rather  than  through  the  sulphuric  acid  in  the  drying 
bottle  until  the  tension  on  the  rubber  bag  is  sufficiently  great  to  force 
the  air  again  through  the  sulphuric  acid  in  the  drying  bottle.  By 
squeezing  the  bag  together  with  the  hands  the  air  can  be  discharged 
again  into  the  drying  bottle  and  thence  into  the  main  air-pipe.  In  so 
doing  there  is  no  gain  or  loss  of  air  to  the  system.  Care  must  be  taken, 
however,  to  see  that  the  pressure  on  the  rubber  bag  is  not  enough  to 
force  the  level  of  the  water  in  the  separating  chamber  B  (fig.  19)  down 
to  such  a  point  that  air  can  escape  along  with  water  through  the  overflow. 

It  has  been  found  by  repeated  tests  that  the  amount  of  air  contained 
by  an  ordinary  foot-ball  bladder  under  the  tension  here  used  is  about 
0.80  liter,  and  this  quantity  of  air  is  removed  from  the  main  air-circuit. 
A  correction  for  this  amount  is  made  in  the  data  for  the  experimental 
period  from  7  a.  m.  to  9  a.  m.,  in  making  which  it  is  customary  to 
assume  that  this  volume  of  air  consists  of  one-fifth  of  oxygen  and  four- 


THE   RESPIRATION   APPARATUS.  53 

fifths  nitrogen,  since  the  actual  composition  rarely  varies  sufficiently 
to  make  any  material  difference  in  the  calculation. 

After  the  sample  is  taken ,  both  pinchcocks  are  closed ,  the  rubber  bag  re- 
moved, and  the  glass  tube  again  dipped  in  water  to  insure  tight  closure. 

In  the  alkaline  pyrogallate  method  of  determining  oxygen  it  is  abso- 
lutely essential  that  the  air  sample  be  free  from  carbon  dioxide.  In  the 
procedure  outlined  above  the  sample  is  taken  after  the  air  has  passed 
through  the  three  U  tubes  for  the  residual  analysis,  and  consequently 
should  be  free  from  carbon  dioxide.  We  have  frequently  tested  the 
efficiency  of  these  U  tubes  for  removing  completely  the  carbon  dioxide 
from  an  air  current  and  have  found  them  to  be  remarkably  satisfactory. 
Furthermore,  it  is  to  be  remembered  that  the  amount  of  residual  carbon 
dioxide  is  usually  low,  and  absorption  is  presumably  correspondingly 
complete.  It  is  therefore  reasonable  to  assume  that  the  air  sample 
is  absolutely  free  from  carbon  dioxide. 

THE  ANALYSIS  OF  AIR. 

The  desirability  of  exact  analysis  of  air  during  the  progress  of  an 
experiment  with  the  respiration  apparatus  has  been  emphasized  on 
page  12.  The  methods  and  apparatus  used  thus  far  in  this  work  are 
essentially  those  outlined  previously  for  analyzing  oxygen,  and  reference 
is  made  in  the  following  description  to  the  illustration  previously  given 
(fig.  16). 

But  in  the  analysis  of  air  certain  refinements  of  the  method  described 
are  necessary.  The  chief  of  these  is  an  accurate  observation  of  changes 
in  temperature  of  the  gas  between  the  time  of  the  first  and  final  readings- 
While  a  variation  in  temperature  of  several  tenths  of  a  degree  could  not 
have  any  appreciable  effect  on  the  small  volume  of  residual  nitrogen 
obtained  in  the  analyses  of  oxygen,  in  air  analyses,  where  the  residual 
nitrogen  amounts  to  about  80  cc.,  fluctuations  in  temperature  will  be 
accompanied  by  marked  fluctuations  in  the  residual  volume.  Further- 
more, fluctuations  in  barometric  pressure,  although  seldom  occurring 
during  the  actual  process  of  analysis,  might  affect  perceptibly  the 
percentage  of  nitrogen. 

The  important  r61e  played  by  temperature  fluctuations  necessitates 
the  use  of  a  thermometer  graduated  in  tenths  of  a  degree  centigrade, 
and  read  with  a  reading  glass  to  o.oi  °.  This  thermometer  is  placed  in 
the  water-jacket  surrounding  burette  B2.  To  insure  a  more  equable 
temperature  of  the  gas  in  the  burettes,  provision  is  made  for  stirring 
the  water  in  the  water-jackets.  A  slow  stream  of  air  is  forced  through 
two  fine  jets  at  the  bottom  of  the  water-jackets,  openings  in  the  corks 
in  the  top  allowing  for  the  free  escape  of  air.  As  the  air  bubbles 
through  the  long  column  of  water,  the  water  is  very  completely  stirred . 


54  A   RESPIRATION   CALORIMETER. 

By  means  of  the  screw  pinchcocks  sl  sz  the  amount  of  air  bubbling 
through  the  water  can  be  regulated  at  will.  Some  difficulty  was  expe- 
rienced in  getting  an  air  pressure  sufficient  to  force  air  through  such  a 
long  column  of  water,  but  compressed  air  from  a  cylinder  was  eventu- 
ally found  satisfactory.  The  air  is  first  saturated  with  water  vapor 
by  bubbling  through  water  in  a  gas-washing  bottle,  thus  diminishing 
the  cooling  effect  in  the  water-jackets  due  to  the  evaporation  of  water. 
In  case  there  is  clogging  of  the  tubes  and  consequent  increased  pressure, 
a  mercury  trap  provides  a  safety  escape. 

Inasmuch  as  the  percentage  of  oxygen  in  the  carbon-dioxide  free  air 
from  the  respiration  chamber  is  seldom  less  than  17  to  1 8  per  cent,  the 
graduations  on  burette  B2,  which  extend  only  from  90  to  100  cc. ,  do 
not  permit  of  reading  directly  the  volume  of  unabsorbed  gas  when  drawn 
from  the  pipette  back  into  B2.  This  volume  may  be  as  great  as  83  cc. 
or  as  small  as  78  cc.  To  overcome  this  difficulty,  we  have  adopted  the 
plan  of  driving  a  definite  volume  of  nitrogen  from  the  burette  Bw 
through  the  3-way  stopcock  C,  into  burette  B2,  in  order  to  depress 
the  level  of  the  water  in  B2  to  such  a  point  that  it  can  be  read  on  the 
graduations  from  90  to  100  cc.  In  general,  about  10  to  14  cc.  of  nitro- 
gen are  thus  expelled  from  the  burette  Bj.  At  the  beginning  of  an 
analysis  the  burette  Bx  is  nearly  filled  with  pure  nitrogen,  obtained 
either  from  a  previous  analysis  of  air  or  from  the  gas  above  the  reagent 
in  the  Hempel  pipette. 

Having  filled  the  burette  El  with  nitrogen,  the  neck  of  the  rubber  bag 
used  to  collect  the  sample  of  air  to  be  analyzed  is  slipped  over  the  end  of 
the  capillary  tube  T.  On  opening  the  stopcock  C  the  air  is  drawn  into 
the  burette  B2  until  the  water  level  in  the  burette  is  the  same  as  that  in 
the  reservoir  R,.  The  stopcock  C  is  then  closed,  the  screw  pinchcock 
on  the  neck  of  the  rubber  bag  closed,  and  the  bag  removed.  Theoreti- 
cally, it  is  better  to  leave  the  bag  on  until  just  before  reading  the  volume, 
but  the  difference  in  composition  of  the  room  air  and  the  small  sample  in 
the  open  portion  of  the  tube  is  so  slight  that  practically  no  difference  in 
results  is  to  be  expected.  After  allowing  the  water  in  burette  B,  to  drain 
down  the  customary  time,  readings  are  taken  of  the  volume  in  the  burette, 
of  the  thermometer,  and  of  the  barometer.  The  gas  is  then  driven  over 
through  the  stopcock  C  into  the  Hempel  pipette  described  for  oxygen 
analysis  (p.  37),  all  the  gas  in  the  capillary  tubes  being  forced  out  by  the 
pressure  of  the  water  in  the  elevated  reservoir  R2.  After  closing  the  stop- 
cock C  and  the  pinchcock  P  on  the  pipette,  the  air  is  shaken  vigorously 
with  the  reagent  for  five  minutes.  The  residual  unabsorbed  gas  is  then 
returned  to  the  burette  Ba,  and  by  lowering  the  reservoir  R2  the  reagent 
is  drawn  up  through  the  rubber  connection  R  and  along  the  capillary 


t 
THE   RESPIRATION  APPARATUS.  55 

to  the  mark  G.  The  volume  of  gas  thus  returned  to  the  burette  must 
be  supplemented  by  a  volume  to  be  delivered  from  the  burette  B,  before 
the  gas  can  be  read  on  B2.  The  reservoir  Rj  is  lowered  until  the  level 
of  the  liquid  in  R:  and  B:  are  the  same.  The  reading  on  B,  is  then 
carefully  noted.  On  raising  R!  and  carefully  opening  stopcock  C  pure 
nitrogen  can  be  driven  over  into  B.2.  It  is  necessary,  however,  that  in 
this  case  the  reservoir  R2  should  be  at  or  about  the  level  shown  in 
figure  1 6.  As  soon  as  sufficient  nitrogen  has  been  forced  into  B2  to 
bring  the  water  level  well  on  the  graduated  portion  of  the  burette  the 
stopcock  C  is  closed.  After  again  adjusting  the  water  levels  in  Rj  and 
BI,  the  reading  of  the  gas  remaining  in  B,  is  made  and  the  difference  in 
volume  subtracted  from  the  final  reading  on  B2.  The  final  readings  of 
volume  and  temperature  are,  of  course,  not  taken  until  the  water  has 
settled  and  drained  down  the  sides  of  the  burette. 

A  specimen  analysis  of  a  sample  of  the  air  taken  from  the  respiration 
chamber  is  given  below  as  illustrating  the  methods  of  analysis.  The 
sample  of  air  was  drawn  at  7  a.  m.  on  April  29,  1904.  The  reading  on 
B,  was  99.25  cc.  -(-  0.51  =  99.76  cc.  The  initial  temperature  was  18.64; 
the  corrected  barometer  reading  was  753.29  mm.  After  absorbing  the 
oxygen  the  gas  was  run  back  into  B2  and  nitrogen  from  Bj  added  to 
this  volume.  The  first  reading  on  E1  was  19.00,  the  second  5.47,  in- 
dicating that  13.53  cc.  of  nitrogen  had  been  added  to  the  volume  of 
the  gas  in  B2.  The  final  reading  on  B,  was  93.89.  On  deducting  the 
J-S-SS  cc-  °f  nitrogen  that  were  added  from  B1}  the  corrected  volume  of 
gas  measured  in  B2  was  80.36.  There  still  remained,  however,  the 
constant  volume  0.34,  which  should  be  added  for  the  gas  remaining  in 
the  stopcock  and  connection  to  graduation  point  G.  The  final  result, 
then,  is  80.36  +  0.34  =  80.70.  The  change  in  temperature  amounted 
to  0.09°,  the  initial  temperature  being  18.64°  an(i  the  final  I8.73°.  In 
increasing  its  temperature  the  gas  has  expanded  and  the  tension  of 
aqueous  vapor  has  increased  slightly  ;  consequently  it  is  necessary  to 
take  into  consideration  its  effect  on  the  tension  of  the  gas  in  the  burette. 
The  tension  of  aqueous  vapor  at  18.64°  is  equal  to  15.96  mm.  of  mer- 
cury. This,  subtracted  from  the  barometric  reading,  753.29,  gives  the 
reduced  pressure  as  737.33  mm. 

The  tension  of  aqueous  vapor  at  18.73°  is  J6.o5  mm.  As  there  was 
no  noticeable  change  in  the  barometric  pressure,  this  tension  is  deducted 
from  the  original  barometric  pressure,  i.  <?.,  753.29,  and  the  resulting 
pressure  is  equal  to  753.29  — 16.05  =  737-24  mm-  Therefore  99.76  cc. 
of  air  at  18.64°  and  737.33  mm.  pressure  yield  80.70  cc.  of  nitrogen  at 
18.73°  and  737.24  mm. 

On  reducing  both  these  gas  volumes  to  standard  conditions  of  tem- 
perature and  pressure  we  find  that  this  particular  sample  of  air  contains 


56  A   RESPIRATION    CALORIMETER. 

80.856  per  cent  of  nitrogen.  A  duplicate  analysis  gave  80.854  Per  cent 
of  nitrogen.  It  is  only  fair  to  state  that  such  an  agreement  is  excep- 
tional rather  than  the  rule.  In  general,  however,  the  agreement  is 
within  0.03  to  0.05  per  cent. 

During  the  process  of  each  analysis  a  small  quantity  of  water  is  un- 
avoidably forced  into  the  pipette,  and  consequently,  while  155  cc.  of 
reagent  will  absorb  nearly  500  cc.  of  oxygen  in  oxygen  analyses,  it 
will  absorb  only  150  cc.  of  oxygen  in  the  air  analyses.  It  seems  reason- 
able to  suppose  that  this  diminished  efficiency  is  due,  in  part  at  least,  to 
the  gradual  dilution  of  the  reagent  by  the  introduction  of  water.  Expe- 
rience has  led  to  the  renewing  of  the  solution  after  eight  analyses  of  air. 

It  can  be  readily  seen  that  this  method  of  analysis,  depending  as  it 
does  on  so  many  readings  of  burettes,  thermometers,  barometer,  etc. , 
is  open  to  serious  objections  when  used  for  the  most  accurate  work.1 
However,  a  series  of  analyses  of  samples  of  outdoor  air  taken  on  suc- 
cessive days  indicated  extremely  close  agreement,  such  as  to  lead  us  to 
believe  that  the  method  is  as  accurate  as  we  can  expect,  in  the  absence 
of  a  constant-temperature  room  and  the  services  of  an  expert  gas  ana- 
lyst, whose  whole  time  can  be  devoted  to  this  kind  of  work. 

ACCESSORY  APPARATUS. 

Aside  from  the  elaborate  respiration  apparatus  proper,  certain  inci- 
dental apparatus  is  necessary,  such  as  balances  for  obtaining  the  weights 
of  gases  absorbed  by  the  residual  U  tubes,  of  the  carbon  dioxide  and 
water  in  the  absorbers,  and  of  the  oxygen,  a  barometer,  and  thermom- 
eters for  determining  the  temperature  of  the  air,  both  in  the  respiration 
chamber  and  in  the  exterior  portions  of  the  air-circuit.  Other  incidental 
apparatus,  which  has,  however,  more  to  do  with  the  measurements  of 
heat  than  of  the  respiratory  products,  will  be  described  hereafter  in 
connection  with  the  discussion  of  heat  measurements. 

BALANCES. 

Analytical. — For  weighing  the  residual  U  tubes  and  all  general  ana- 
lytical work  in  the  laboratory,  in  connection  with  experiments  with 
the  respiration  calorimeter,  short- beam  analytical  balances  of  standard 
types  are  used. 

Balance  for  weighing  the  carbon-dioxide  and  water  absorbers  and  oxygen 
cylinders. — The  quantitative  determination  of  the  total  carbon  dioxide, 
water,  and  oxygen  in  the  air  current  necessitates  the  use  of  a  balance  at 

*At  the  moment  of  writing  there  is  being  installed  in  this  laboratory  the  form  of 
air-analysis  apparatus  used  by  Zuntz  in  his  work  on  the  respiratory  exchange. 


ACCESSORY   APPARATUS.  57 

once  sufficiently  strong  to  stand  the  weight  of  the  individual  members  of 
the  absorbing  system  and  of  the  oxygen  cylinders  and  at  the  same  time 
sufficiently  sensitive  to  note  a  slight  increase  in  weight  with  great  accu- 
racy. The  heaviest  individual  members  of  the  absorbing  system  are  the 
water-absorbers,  which  weigh,  after  the  absorption  of  one-half  kilogram 
of  water,  not  far  from  16  to  18  kg.  The  balance  now  in  use  for  this 
purpose  was  obtained  from  the  firm  of  Dr.  Robert  Muencke,  of  Berlin, 
through  the  Bausch  &  L,omb  Optical  Company,  of  Rochester,  New  York. 
It  is  shown  in  figure  2 1 . 

The  water  and  carbon -dioxide  absorbers  and  oxygen  cylinders  are 
too  large  to  be  placed  directly  upon  the  balance-pan  for  weighing ;  con- 
sequently the  balance  is  so  mounted  that  it  is  possible  to  suspend  each 
separate  member  on  a  wire  fastened  to  one  arm  of  the  balance.  As  is 
shown  in  figure  21,  the  balance  is  mounted  on  a  heavy  shelf  fastened 
securely  to  the  brick  wall.  The  left-hand  hanger  of  the  balance  has 
been  removed  and  is  replaced  by  a  phosphor-bronze  wire  which  extends 
through  a  hole  in  the  bottom  of  the  balance-case,  and  is  provided  with 
hooks  or  loops  for  suspending  the  objects  to  be  weighed. 

Since  changes  in  weight  are  here  desired,  rather  than  absolute  weight, 
the  larger  part  of  the  weight  of  these  objects  is  balanced  with  lead  coun- 
terpoises. The  glass  front  of  the  balance-case  can  be  raised  and  the 
counterpoises  added  or  removed  as  desired. 

To  prevent  the  effect  of  air  currents  along  the  floor,  the  lower  part  of 
the  balance,  i.  e.,  the  portion  beneath  the  shelf,  is  inclosed  as  a  closet. 
The  framework,  however,  does  not  come  in  contact  with  the  shelf,  there 
being  a  small  air  gap  between  to  eliminate  the  transmission  of  vibration 
from  the  floor  to  the  shelf.  The  front  of  the  closet  consists  of  two  doors, 
one  of  which  is  removed  in  figure  21.  To  provide  illumination  a  glass 
window  is  placed  in  the  left-hand  side,  and  the  whole  interior  is  painted 
white.  On  dark  days  or  during  the  night  an  electric  light  is  inserted. 

A  small  piece  of  plate  glass  is  set  in  the  shelf  immediately  in  front  of 
the  balance  in  such  a  way  that  the  upper  surface  of  the  glass  is  just 
flush  with  the  top  of  the  shelf.  After  the  doors  of  the  closet  have  been 
closed  it  is  possible  for  the  assistant  to  look  through  this  glass  and  see 
that  the  object  to  be  weighed  is  freely  suspended. 

The  phosphor-bronze  wire  by  which  the  objects  are  suspended  is 
permanently  fastened  to  the  hanger  on  the  left-hand  balance-arm.  The 
lower  end  is  provided  with  a  swivel,  to  which  two  wires  with  small 
hooks  on  the  end  are  attached.  These  hooks  can  be  conveniently 
attached  to  the  handles  of  the  water-absorbers.  (See  fig.  n.) 

In  weighing  these  heavy  objects  it  was  found  much  more  convenient 
to  place  them  first  on  a  small  platform  which  could  be  raised  sufficiently 


58  A    RESPIRATION   CALORIMETER. 

to  allow  the  hooks  from  the  suspension  wire  to  be  readily  slipped  under 
the  handles  of  the  absorber.  By  means  of  the  wooden  lever  at  the  left- 
hand  side  of  the  weighing  closet,  the  movable  platform  on  which  the 
absorber  is  placed  can  then  be  lowered  slowly,  thus  gradually  shifting 
the  weight  to  the  wires.  When  the  wooden  handle  is  in  an  upright 
position,  the  movable  platform  or  elevator  is  at  its  lowest  point,  and  the 
object  to  be  weighed  swings  freely  above  it.  A  simple  clutch  holds  the 
lever  firmly  when  it  is  sustaining  the  weight  of  the  absorber,  and  all 
that  is  necessary  to  release  the  clutch  is  to  push  the  handle  forward  a 
short  distance. 

The  bracket-arm  fastened  to  the  lever  has  two  chains  attached  to  its 
outer  end  ;  these  travel  through  pulleys  in  the  top  of  the  closet  and  are 
so  adjusted  that  both  sides  of  the  elevator  are  lowered  to  the  same  dis- 
tance and  simultaneously,  thus  making  an  even  up-and-down  motion. 
The  details  of  this  apparatus  are  shown  in  figure  2 1 . 

After  weighing,  the  lever  at  the  left  of  the  balance  is  pushed  for- 
ward, thus  taking  the  weight  off  the  wire.  The  hooks  can  then  be 
unfastened  and  the  absorber  readily  withdrawn. 

For  weighing  the  carbon-dioxide  absorbers,  two  copper  loops  act  as 
extensions  to  the  steel  hooks.  A  similar  device  serves  for  suspending 
the  oxygen  cylinders. 

One  of  the  most  striking  features  of  this  balance  is  its  great  capacity 
and  extreme  sensitiveness.  In  weighing  the  water- absorbers,  some  of 
which  weigh  fully  1 8  kg. ,  we  have  the  greatest  test  on  the  sensitiveness 
of  the  balance,  and  it  is  found  that  these  absorbers  may  be  weighed 
so  delicately  that  a  difference  of  20  mg.  is  readily  detected — a  degree  of 
accuracy  far  beyond  the  ordinary  requirements. 

A  balance  of  the  same  type,  but  with  one-half  the  capacity,  i.  <?.,  ickg. 
in  each  pan,  is  employed  for  weighing  food,  feces,  urine,  and  miscel- 
laneous small  articles  used  in  connection  with  experiments  on  man. 
This  balance  is  so  accurate  and  so  sensitive  that  it  can  be  used  for 
adjusting  large  weights,  and  by  a  method  of  double  weighing  we  have 
standardized  with  it  all  of  our  weights  over  200  grams,  and  determined 
the  actual  weight  of  the  different  counterpoises  used  on  the  water-meter 
(see  p.  126)  and  large  balance. 

WEIGHTS. 

The  accuracy  of  the  determination  of  the  balance  of  intake  and  out- 
put of  matter  with  the  respiration  calorimeter  obviously  depends  on  the 
accurate  weighing  of  the  factors  of  income  and  outgo.  The  materials 
of  the  income  are  weighed  usually  on  a  sensitive  balance  with  one  set  of 
weights,  the  samples  for  analyses  weighed  on  an  analytical  balance  with 


TO  face  page  58. 


FIG.  21.— Balance  for  Weighing  Absorbers  and  Oxygen  Cylinders.  The  absorbers  are  suspended  on 
a  wire  from  left-hand  arm  of  balance,  and  lead  counterpoises  are  used  on  right  side.  Doors  inclose 
weighing  chamber  and  prevent  drafts.  The  lever  on  outside  at  the  left  actuates  the  elevator,  which 
raises  or  lowers  the  absorbers  iu  weighing  chamber. 


ACCESSORY  APPARATUS.  59 

a  second  set  of  weights,  and  the  water,  carbon  dioxide,  and  oxygen 
weighed  on  a  third  balance  with  a  third  set  of  weights. 

Other  weighings  entering  into  the  complete  balance  of  energy,  as 
well  as  of  matter,  are  the  weights  of  water  used  to  bring  away  the  heat 
from  the  apparatus,  and  in  the  bomb  calorimeter  for  measuring  the 
energy  of  income,  and  the  weights  used  on  a  platform  balance  (fig.  46) 
for  weighing  a  man.  With  such  a  system  of  balances  and  weights,  it 
is  obviously  necessary  that  all  weights  should  be  on  some  standard 
basis.  We  have  imported  from  Germany  a  set  of  gold-plated  weights 
ranging  from  i  mg.  to  i  kg.,  and  all  of  our  different  sets  of  weights 
have  been  carefully  calibrated  with  this  set,  which  is  used  only  for  a 
standard.  Consequently  all  weights  used  in  the  experimenting  with 
the  respiration  calorimeter  are  reduced  to  the  same  basis.  The  weights, 
as  well  as  the  sensitiveness  and  accuracy  of  the  balances,  are  tested 
periodically  every  six  months  and  proper  adjustments  made. 

The  individual  weights  of  the  standard  set  have  been  compared  with 
each  other  frequently  in  all  possible  combinations,  and  the  agreement  is 
in  all  cases  very  close.  There  has  been  no  comparison  with  any  abso- 
lute standard,  as  practically  all  of  our  work  depends  upon  differences  in 
weight  rather  than  absolute  weight.  We  have,  however,  no  reason  to 
doubt  the  accuracy  of  the  standard  weights  as  furnished  us,  for  when 
compared  with  numerous  new  sets  of  analytical  weights  no  noticeable 
differences  have  been  found.  Apparently  the  analytical  weights,  though 
from  several  manufacturers,  must  have  been  referred  to  standards 
agreeing  very  closely  with  each  other. 

With  the  larger  weights  used  for  weighing  food  and  the  absorbing 
apparatus  of  the  respiration  chamber,  the  adjustment  was  found  to  be 
much  more  readily  made  if  the  handle  or  top  of  the  weight  screwed 
into  the  base.  Accordingly  a  number  of  sets  of  weights  were  made 
in  the  mechanical  laboratory  of  Wesleyan  University  on  this  plan, 
and  consequently  the  work  of  delicate  adjustment  is  reduced  to  a 
minimum. 

For  calibrating  the  larger  weights,  200  grams  and  over,  the  balances 
described  on  page  58  were  used,  after  making  all  due  precautions  and 
interchanging  weights  from  one  pan  to  the  other. 

All  the  weighings  and  measurements  are  made  at  the  same  level  in 
the  calorimeter  room,  which  has  an  elevation  of  48.8  meters  above  sea 
level.  The  latitude  of  Middletown  is  41°  34'.  It  has  been  found 
that  to  correct  all  weighings  to  standard  gravity,  i.  <?.,  latitude  45°, 
would  involve  a  large  amount  of  unnecessary  labor.  The  actual  cor- 
rection is  only  about  three  parts  in  10,000,  representing  a  degree  of 
refinement  that  is  far  removed  from  many  of  the  operations  in  connection 


60  A   RESPIRATION   CALORIMETER. 

with  the  experimental  work  with  the  respiration  calorimeter.  For  this 
reason,  where  it  is  necessary  to  make  comparisons  of  weights  and  vol- 
umes of  gases,  the  relations  are  calculated  for  the  latitude  and  elevation 
of  the  calorimeter  laboratory.  For  similar  reasons,  weights  are  not 
reduced  to  vacuum. 

THE   BAROMETER. 

With  the  volume  of  air  confined  in  the  apparatus,  amounting  to  about 
5,000  liters,  slight  variations  in  barometric  pressure  will  make  relatively 
large  variations  in  the  apparent  volume  of  the  air  in  the  system.  A 
variation  in  barometric  pressure  of  i  mm.  of  mercury,  or  i  part  in  760, 
is  accompanied  by  a  variation  amounting  to  about  7  liters  in  the  apparent 
volume  of  air.  Consequently  it  is  necessary  that  the  barometric  pressure 
be  known  as  accurately  as  possible. 

Through  the  kindness  of  Mr.  Willis  L.  Moore,  chief  of  the  Weather 
Bureau  of  the  United  States  Department  of  Agriculture,  at  Wash- 
ington, a  barometer  was  loaned  for  use  in  connection  with  these  experi- 
ments. The  barometer  was  brought  to  Middletown  by  Prof.  Charles 
F.  Marvin,  of  the  instrument  division  of  the  Weather  Bureau,  who 
personally  superintended  its  installation.  This  instrument  is  of  the 
Fortin  type,  capable  of  being  read  with  a  vernier  to  o.ooi  inch.  It  is 
mounted  with  two  white  backgrounds,  consisting  of  two  sheets  of  paper, 
behind  which  two  incandescent  lamps  are  placed.  When  the  lamps  are 
lighted  a  brilliantly  illuminated  field  gives  excellent  opportunity  for 
adjusting  the  vernier  at  the  top.  The  box  in  which  the  barometer  is 
hung  is  firmly  supported  on  two  uprights  extending  from  the  floor  to 
the  ceiling  of  the  laboratory.  The  relative  position  of  the  barometer 
to  the  rest  of  the  apparatus  is  shown  in  figure  i . 

Tables  giving  corrections  for  the  barometer  and  for  the  attached 
thermometer  were  furnished  by  the  U.  S.  Weather  Bureau,  and  before 
being  brought  to  Middletown  the  instrument  was  carefully  adjusted 
under  Professor  Marvin's  supervision.  Its  accuracy  is  all  that  could  be 
desired. 

The  correction  for  the  scale  errors  and  capillarity  of  this  instrument 
amounts  to  +  0.002  inch  and  the  correction  for  local  gravity  at  the 
latitude  of  Middletown,  41°  34',  is  — 0.009  inch,  making  the  total  cor- 
rection —  0.007.  As  will  be  noted  later,  however,  it  is  found  to  simplify 
calculations  if  the  corrections  for  gravity  are  not  applied,  and  in  practice 
the  correction  used  is  +  002  inch. 

The  thermometer  attached  to  the  barometer  has  only  insignificant 
corrections  for  that  portion  of  the  scale  on  which  readings  are  usually 


ACCESSORY  APPARATUS.  6 1 

made,  and,  as  it  need  be  read  only  to  the  nearest  half  degree,  no 
corrections  are  made.  Consequently  to  facilitate  in  the  calculations, 
reference  is  made  to  tables  giving  the  true  correction  to  be  deducted  in 
every  case  from  the  actual  reading  of  the  barometer  and  for  every 
half  inch  difference  in  the  height  of  the  barometer  and  for  every  half 
degree  difference  in  the  temperature.  The  correction  as  recorded 
on  this  table  is  the  standard  temperature  correction  for  reducing  the 
mercury  column  minus  the  scale  error  and  capillarity  correction  of  this 
special  barometer  (0.002  inch),  as  mentioned  above.  To  facilitate  the 
calculations,  the  corrected  reading  of  the  barometer  is  converted  by 
means  of  a  table  to  the  metric  reading  in  one-hundred ths  of  a  millimeter. 

OBSERVATION  OF   TEMPERATURE. 

The  total  air  in  the  closed  circuit  may  be  considered  as  being  made 
up  of  two  portions.  The  larger  portion,  amounting  to  about  5,000 
liters,  is  that  in  the  respiration  chamber  proper  ;  the  remaining  portion, 
of  about  62  liters,  is  that  contained  in  the  air-pipe,  absorbing  system, 
pump,  and  pans.  (See  p.  70.) 

The  air  in  the  chamber  is  maintained  at  a  fairly  constant  temperature 
as  a  result  of  the  heat-regulation  devices  described  elsewhere  (p.  124). 
The  temperature  is  recorded  quite  accurately  by  means  of  the  electrical 
resistance  thermometers  (p.  I35).1  These  thermometers  are  assumed  to 
give  the  temperature  of  the  air  within  0.01°.  In  addition,  a  mercury 
thermometer,  graduated  to  tenths  of  degrees,  is  suspended  in  the  cham- 
ber near  the  window  as  a  guide  to  the  actual  temperature  expressed  in 
degrees  centigrade. 

The  air  outside  the  chamber  is  subject  to  a  number  of  temperature 
fluctuations.  As  has  been  described,  the  calorimeter  laboratory  is 
heated  by  steam-pipes  suspended  near  the  top  of  the  room.  Conse- 
quently a  very  great  difference  in  temperature  exists  between  the  air  at 
the  level  of  the  absorbing  system  and  that  of  the  pipes  conducting  the 
air  to  and  from  the  chamber.  To  obtain  the  temperature  of  these 
portions  of  the  system,  we  rely  upon  other  mercurial  thermometers. 
One  is  attached  to  the  outside  of  the  chamber,  so  as  to  hang  just  in 
front  of  the  window.  A  second  thermometer  kis  suspended  near  the 
pans,  so  that  the  bulb  is  on  a  level  with  the  horizontal  air-tube.  A 
third  thermometer,  the  bulb  of  which  is  immersed  in  the  water  in  the 
Elster  meter,  gives  the  temperature  of  the  air  sample.  These  ther- 
mometers are  designated  respectively  as  T,  T1;  and  Tm.  The  first  two 

1  For  a  discussion  of  the  significance  of  the' temperature  measurements  by  these 
thermometers,  see  page  91. 


62  A   RESPIRATION   CALORIMETER. 

thermometers  are  graduated  in  degrees  and  read  to  tenths  of  a  degree. 
That  used  in  the  Elster  meter  is  read  to  hundredths  of  a  degree.  As 
the  temperatures  at  which  they  are  used  rarely  exceed  25°,  it  was  found 
expedient  to  calibrate  them,  together  with  a  number  of  others  used  for 
incidental  work,  such  as  in  the  specific  gravity  of  alcohol,  etc.,  simul- 
taneously with  the  water  thermometers,  and  a  table  of  corrections  for 
each  thermometer  in  use  in  the  laboratory  was  thus  obtained  under  con- 
ditions exactly  similar  to  those  described  for  the  water  thermometers. 
(See  p.  133.)  All  temperatures  read  by  observers  are  subject  to  these 
corrections  before  use  in  the  calculations. 

In  regard  to  the  temperature  observations  on  that  portion  of  the  air- 
circuit  outside  of  the  respiration  chamber,  it  is  found  that  under  certain 
conditions  of  experimenting,  especially  those  in  which  large  quantities 
of  carbon  dioxide  are  being  absorbed,  the  temperature  of  the  carbon- 
dioxide  absorbers  is  considerably  increased.  In  one  experiment  the 
bulb  of  a  thermometer  was  placed  on  the  exterior  of  the  absorber,  the 
bulb  covered  with  a  piece  of  hair  felt,  and  the  temperature  noted.  A 
temperature  of  47.5°  was  observed  during  this  experiment,  and  an 
observation  on  another  day  gave  a  temperature  of  53.3°. 

As  stated  previously  (p.  31),  all  three  carbon-dioxide  absorbers  dur- 
ing a  work  experiment  become  more  or  less  heated,  although  usually 
the  excessive  heat  is  confined  to  one  absorber.  In  consideration  of  the 
lack  of  more  data,  it  has  been  assumed  that,  while  the  carbon  dioxide 
was  being  absorbed  from  the  air  current  during  a  period  in  which  the 
subject  was  engaged  in  excessive  muscular  exercise,  one-half  of  the  air 
in  the  soda-lime  absorbers  reached  a  temperature  of  50°,  the  rest 
remaining  at  20°.  It  has  been  computed  that  about  0.4  liter  of  air  is 
thereby  added  to  the  system  at  each  change  in  the  absorbing  system 
after  a  period  of  heavy  work.  In  an  alcohol  check  experiment,  or  in  a 
rest  experiment,  the  rise  in  temperature  is  so  slight  that  no  correction 
is  necessary. 

In  the  first  water-absorber  there  is  always  a  slight  rise  in  temperature 
above  the  initial  temperature.  The  amount  of  water  absorbed  in  the 
course  of  a  two-hour  period  is  too  small,  however,  to  cause  any  great 
increase  in  temperature,  and  consequently  it  is  not  considered  in  the 
calculations. 


CALCULATION   OF   RESULTS.  63 

CALCULATION  OF  RESULTS. 

The  ultimate  object  of  the  respiration  apparatus  and  the  accessory 
appliances  is  to  obtain  an  accurate  measure  of  the  respiratory  products, 
i.  e, ,  the  carbon  dioxide  and  water  vapor  eliminated  and  the  oxygen 
consumed.  The  data  obtained  with  the  apparatus  are  the  weights  of 
carbon  dioxide  and  water  absorbed  in  the  absorbing  system,  the  weight 
of  oxygen  supplied  to  the  ventilating  current  of  air,  and  the  incidental 
physical  measurements,  such  as  the  temperatures  of  the  different  masses 
of  air  comprising  the  system,  and  the  barometric  pressure.  If  the  vari- 
ations in  composition  of  the  residual  amounts  of  air  were  entirely  neg- 
lected, the  total  carbon-dioxide  and  water  output  and  oxygen  intake 
could  be  determined  readily  by  noting  the  increase  in  weight  of  the 
absorbers  and  the  loss  in  weight  of  the  oxygen  cylinders.  For  conven- 
ience in  calculation,  the  data  obtained  from  the  absorbers  and  oxygen 
cylinders,  and  also  the  data  regarding  the  residual  analyses,  together 
with  the  temperature  observations  and  positions  of  the  rubber  dia- 
phragms on  the  pans,  are  recorded  on  a  special  blank,  a  specimen  of 
which  is  given  on  the  following  page. 

AMOUNT   OP   WATER   ABSORBED. 

Assuming  that  there  are  no  changes  in  the  amount  of  moisture  in 
the  residual  air,  the  amount  of  water  vapor  eliminated  per  period 
corresponds  to  the  gain  in  weight  of  the  first  water-absorber. 

By  reference  to  the  blank,  it  will  be  seen  that  in  the  experiment  here 
used  the  absorber,  which  was  No.  5,  weighed  at  the  start,  aside  from 
the  weight  of  the  counterpoises,  3,296.0  grams.  At  the  end  of  the 
period,  which  in  this  particular  instance  was  of  two  hours'  duration 
and  ended  at  7  a.  m.,  April  9,  1905,  the  absorber,  when  removed  from 
the  system,  weighed  3,350.8  grams,  the  increase  in  weight  during  this 
two-hour  period  being,  therefore,  54. 8  grams.  While  this  may  be  taken 
as  an  estimate  of  the  weight  of  water  absorbed  during  this  period,  there 
are  two  corrections  to  be  applied  independent  of  any  correction  for  the 
variation  in  composition  of  the  residual  air.  In  the  first  place,  a  small 
amount  of  water  is  actually  absorbed  in  the  U  tubes  used  for  residual 
analysis,  and  thus  removed  from  the  ventilating  air  current.  In  this 
instance  the  amount  of  water  in  the  two  tubes  was  o.  1 1  gram.  Fur- 
thermore, as  was  explained  on  page  26,  owing  fo  the  transudation  of 
acid  through  the  absorbers  during  the  time  that  these  particular  data 
were  obtained,  they  were  absorbing  a  small  amount  of  water  from  the 
external  air  of  the  laboratory,  which  has  been  very  closely  determined 
to  be  0.20  gram  per  two-hour  period,  and  consequently  the  increase  in 
weight  of  this  absorber  is  too  large  by  o.  20  gram.  The  corrected  weight 
of  water  absorbed  during  this  period,  accordingly,  is  54.71  grams. 


A   RESPIRATION   CALORIMETER. 

Calculations  for  Carbon  Dioxide,  Water,  and  Oxygen.    No.  16. 
7.00  a.  m.,  April 9,  1905.    Residual  at  end  of  I2th  period.    Metabolism  expt.  No.  77. 


FIRST  RESIDUAL. 

SECOND  RESIDUAL. 

OXYGEN. 

9.958  liters. 
Tin,          =  20.69 

10.016  liters. 
Tm,               =     20.68 

Cylinder  No.  32888       Log.        $    N.  =  15838 
Weight  on        i846.oo        "       O  +  N.  =  67006 

Cor.  Tm,  =  20.45 
Water  Man.  =    149 
10.30 
.66 

Cor.  Tm,     =     20.44 
Water  Man.       =       167 
11.77 
•51 

Grams  O.+  N.     46.78                                 90018 
N.         .67                                    

O.     46.11    Inters          N.              .54 

Cylinder  No.                  Log.        $    N.  = 
Weight  on                          "       O  +  N.  = 

Hg  =  1096 
H,S04       J         72.3788 
No.  9         I        72-3249 
Weight  HSO          .0539 
S.  I,.       [        78.9948 
N           \        78-9696 

Hg=    12.28 
JH,S04           (              72-6625 
No.  2            (              72.6071 
Weight  HjO  —             -0554 

"    gnis.  N.  = 
Grams  O.+  N.                                              90078 

S.  L.         (              73-3793 
E              (             73.3507 

O.                Liters         N. 

Cylinder  No.                   Log.        %   N.  = 
Weight  on                          "       O  +  N.  = 
"        off 
"    gms.  N.  = 
Grams  O.+  N.                                              9OOT8 
"               N.                                                 
"    liters  N.= 
O.                Liters         N. 

Cylinder  No.                   Log.        %   N.  = 
Weight  on                          "       O  +  N.  = 
"       off 

.0252 
H,SO4        (        67.7512 
No.  19        I         67.7342 
.0170 

S.   L.                                    .0252 

.0286 
H2SO4           (              76.6298 
No.  13           (              76.6143 

•0155 
S.  L.                            -0286 

Total  COj              .0422 
To    —    20.79 

TI     =      20.O        =       20.0 

Total  CO,                      .0441 

Pan  No.  i  =  575        =  11.2 
Pan  No.  2  =  empty  =    2.5 

13-7 

Grams  O.  +  N.                                              90018 
"              N.                                              
"     liters  N.= 
O.                Liters         N. 

CO,  &  HaO 

H,SO4      (End        3350.8                   HaO  total, 
-s                                                                  54-8 
No  5        (start       3296.0                                        .n 

Grams  Oxygen              Liters  Nitrogen 

46.11  Cylinder                                .54  ToUl. 

54 
S.  L.     (End        2422 
S           (.Start       2416 

54-71 
7                                          -7 

46.07  Total. 

2                                   38.297 

AIR  REJECTED  AT  M. 

6.5                      air  displaced 

S.  L.     (End        2740.9                   CO,  total, 
•s                                                                   6-5 
L           (Start       2722.1                                     18.8 

liters 

Tm,                —             Log.  L. 
Cor.               =             Cor. 

Cor.  Tm,       =             Temp. 
Pressure  .  - 

18.8                                       16.3 
.09 
S.  I,.     (  End        3284.7                Cor.       —       .20 

I           (start      2282.2                                   43.99 

Water  Man.  —            O.+N.              =       L. 
Log.jiN.  
N.-   ....--       L. 

2.5                 Resp.  loss 
S.  L-     ("End 
•<                                        CO,        =        43.99 
I  Start                            HaO      =       54.71 

Hg      .      .      =              O      L. 

e  @  Tm,        -= 

HaSO4      (End        3525 
No.  6       (Start       3508 
16 

o              Sum      =       98.70 
Less  O  =       46.07 

Sum       .       = 
Barometer   = 

Difference    =- 

Diff       =       52.63 
3                            =    .05!,. 

CALCULATION    OF   RESULTS.  6«> 

AMOUNT    OF   CARBON   DIOXIDE   ABSORBED. 

The  weight  of  carbon  dioxide  absorbed  was  determined  by  noting  the 
increase  in  weight  of  each  of  the  three  soda-lime  cylinders  S,  L,  and  I  and 
the  water-absorber  No.  6,  through  which  the  air  passed  after  leaving  the 
soda-lime  cylinders.  Soda-lime  cylinder  S  weighed  at  the  start  2,416.2 
grams  more  than  the  counterpoise.  At  the  end  of  two  hours  it  was  ob- 
served that  the  weight  had  increased  by  6. 5  grams.  Similarly ,  cylinder  I, 
had  increased  in  weight  1 8 . 8  grams  and  cylinder  12.5  grams,  while  water- 
absorber  No.  6  had  increased  in  weight  16.3  grams.  To  find  the  total 
weight  of  carbon  dioxide  during  this  period,  therefore,  the  increases  in 
weight  of  these  four  parts  of  the  carbon-dioxide  absorbing  system  were 
added  together,  the  amount  of  carbon  dioxide  absorbed  in  the  two  re- 
sidual analyses,  i.  e.,  0.09  gram,  added,  and  the  usual  correction  of  0.20 
gram  for  the  increase  in  weight  of  absorber  No.  6  subtracted.  It  is 
thus  seen  that  the  total  weight  of  carbon  dioxide  absorbed  during  this 
period  was  43.99  grams.  It  will  be  noted  on  the  blank  that  space  is  left 
for  a  fourth  soda-lime  cylinder.  Frequently,  in  experiments  in  which 
there  is  an  excessive  amount  of  carbon  dioxide  absorbed,  it  becomes 
necessary  to  stop  the  air  current  for  a  moment  or  two  and  replace  an 
exhausted  soda-lime  cylinder  with  a  fresh  one. 

AMOUNT  OF  OXYGEN  ADMITTED. 

The  calculation  of  the  weight  of  oxygen  admitted  to  the  chamber  is 
c  arried  out  on  the  upper  right-hand  side  of  the  blank.  To  avoid  errors 
and  to  aid  in  referring  to  the  cylinder,  the  cylinder  number  is  first  re- 
corded. The  weight  of  the  cylinder  over  and  above  the  counterpoise  at 
the  beginning  of  the  period  and  the  weight  under  the  same  conditions 
at  the  end  are  recorded  immediately  beneath  this.  The  difference, 
which  represents  the  loss  in  weight  of  the  cylinder,  is  the  weight  of  the 
oxygen  plus  the  nitrogen,  for,  owing  to  the  purifying  attachments  on 
the  cylinder  itself ,  the  gas  issuing  from  the  rubber  tube  consists  only  of 
oxygen  and  nitrogen.  It  becomes  necessary,  therefore,  to  calculate  the 
amount  of  nitrogen  admitted  with  this  oxygen,  and  this  is  done  by 
adding  the  logarithm  of  the  percentage  of  nitrogen  of  this  particular 
cylinder,  as  determined  by  the  analysis  (see  p.  34),  to  the  logarithm  of 
the  weight  of  oxygen  and  nitrogen  admitted.  The  sum  of  these  loga- 
rithms is  the  logarithm  of  the  weight  of  nitrogen,  which,  in  this  in- 
stance, amounted  to  0.67  gram,  and,  since  the  weight  of  the  oxygen 
plus  the  nitrogen  was  46.78  grams,  the  true  weight  of  oxygen  admitted 
during  this  period  was  46.11  grams. 

For  purposes  of  calculation,  to  be  explained  beyond  (p.  88),  it  is 
desirable  to  know  the  volume  of  nitrogen  admitted  to  the  chamber, 


66  A   RESPIRATION   CALORIMETER. 

and  consequently  at  this  point  the  calculation  converting  the  weight 
in  grams  of  nitrogen  to  liters  is  made.  This  calculation  is  based  on  the 
relations  between  the  weights  and  volumes  of  gases  as  discussed  on 
page  82,  and  is  here  simplified  by  adding  the  logarithmic  factor  .90078 
to  the  logarithm  of  the  weight  of  nitrogen  in  grams.  It  is  thus  seen 
that  the  volume  of  nitrogen  admitted  with  the  oxygen  in  this  case  was 
o.  54  liter.  On  the  blank  a  space  is  left  for  several  calculations  of  this 
nature,  as  it  frequently  happens  that  more  than  one  cylinder  of  oxygen 
is  used  during  an  experimental  period.  The  oxygen  is  always  admitted 
as  long  as  it  will  flow  from  the  cylinder,  and  even  in  ordinary  rest  exper- 
iments it  is  rare  that  the  last  of  a  cylinder  of  oxygen  is  coincident  with 
the  end  of  an  experimental  period.  During  excessively  hard-work 
experiments,  several  cylinders  may  be  used.  In  case  more  than  one 
cylinder  is  used,  the  weights  of  oxygen  and  liters  of  nitrogen  are  footed 
up  at  the  bottom.  Furthermore,  a  slight  constant  correction,  amount- 
ing to  —  0.04  gram  of  oxygen  (see  p.  74),  is  made  for  certain  alterations 
in  volume,  due  either  to  interchange  of  air  through  the  food  aperture  or 
opening  and  closing  of  mercury  valves,  which  correction,  for  the  sake 
of  convenience,  is  made  on  this  sheet.  During  this  period  we  find  that 
the  total  amount  of  oxygen  admitted  is  46.07  grams. 

It  is  thus  seen  that,  when  no  reference  is  made  to  the  variations  in 
composition  of  the  residual  air,  the  amount  of  carbon  dioxide  and  water 
eliminated  per  given  period  and  the  amount  of  oxygen  absorbed  may  be 
determined  from  the  weights  of  water  and  carbon  dioxide  taken  up  by 
the  absorbing  system  and  the  weight  of  oxygen  admitted  from  the  steel 
cylinder,  with  due  allowance  for  the  accompanying  weight  of  nitrogen. 

RESIDUA!,  ANALYTICAL  DATA. 

The  data  for  the  two  residual  analyses  are  likewise  recorded  side  by 
side  on  this  sheet.  They  include  the  amount  of  air  passing  through 
the  meter,  the  temperature  of  the  meter,  correction  for  the  thermometer 
used  in  the  meter,  pressure  on  the  meter  expressed  in  millimeters  of 
water  as  read  on  the  manometer,  its  conversion  to  millimeters  of  mer- 
cury, and  the  gains  in  weight  of  the  U  tubes  used  for  analysis.  Beneath 
the  record  of  these  data  are  placed  the  temperature  records  and  the 
position  of  the  pans.  When  the  thermometer  has  a  correction,  the 
corrected  temperature  is  placed  at  the  right  of  that  observed.  In  this 
instance  the  thermometer  had  a  zero  correction.  Pan  No.  2  was  empty, 
and  in  this  position  it  is  assumed  that  2.5  liters  of  air  are  inclosed  by  this 
pan,  diaphragm,  and  pipes.  (Seep.  41.)  The  pointer  on  the  wheel  of 
pan  No.  i  stood  at  the  graduation  575,  and  from  a  previously  prepared 
table  it  is  found  that  at  this  position  the  rubber  diaphragm,  pan,  and 


CALCULATION  OP   RESULTS.  67 

pipe  inclosed  11.2  liters  of  air,  thus  making  a  sum  total  of  13.7  in  the 
tension  equalizing  system . 

DATA    FOR  THE   REJECTION   OP  AIR. 

As  the  amount  of  nitrogen  in  the  system  gradually  accumulates  dur- 
ing an  experiment,  by  reason  of  the  fact  that  the  admission  of  oxygen 
is  unavoidably  accompanied  by  an  admission  of  nitrogen,  it  becomes 
necessary  from  time  to  time  to  reject  a  considerable  volume  of  air,  vary- 
ing from  30  to  70  liters,  by  drawing  it  through  the  Elster  meter,  and  to 
replace  it  with  oxygen.  The  calculations  by  which  the  exact  amount 
of  air  thus  rejected  is  determined  are  made  in  the  lower  right-hand 
corner  of  this  sheet.  Here  are  recorded  the  time  at  which  the  air  is 
rejected,  the  number  of  liters  passing  through  the  meter,  the  thermom- 
eter reading  and  correction  for  the  thermometer  in  the  meter,  the  water 
manometer,  with  its  equivalent  in  mercury,  the  tension  of  aqueous 
vapor  at  the  temperature  of  the  meter,  and  the  barometer  reading.  It 
is  thus  possible  to  calculate  the  corrected  volume  of  oxygen  and  nitro- 
gen rejected.  The  proportions  of  oxygen  and  nitrogen  in  this  corrected 
volume  are  obtained  from  the  analysis  of  air  taken  immediately  before 
the  air  is  rejected.  (See  p.  77.) 

CORRECTIONS    FOR    VARIATIONS    IN    VOLUME    AND    COMPOSITION     OP 

RESIDUAL  AIR. 
NECESSITY  FOR  RESIDUAL  ANALYSES. 

The  amounts  of  carbon  dioxide  and  water  eliminated  and  oxygen 
absorbed  as  determined  by  the  gains  in  weight  of  the  absorbing  system 
and  the  loss  in  weight  of  the  oxygen  cylinder,  with  due  corrections  for 
nitrogen,  give,  on  the  whole,  a  general  approximation  of  the  amounts  of 
carbon  dioxide  and  water  eliminated  and  oxygen  absorbed  by  the  sub- 
ject ;  but  in  this  calculation,  as  has  been  pointed  out,  no  notice  is 
taken  of  the  alterations  in  composition  of  the  residual  volume  of  air. 
The  chief  factors  influencing  such  variations  are  muscular  activity  of 
the  subject  with  its  consequent  fluctuations  in  carbon-dioxide  and  water 
production  and  oxygen  absorption,  rapidity  of  ventilation,  and  baro- 
metric pressure. 

The  fluctuations  in  the  amounts  of  carbon  dioxide  and  water  are  in 
the  main  of  a  temporary  nature.  There  may  be  variations  of  over  100 
grams  of  carbon  dioxide  and  20  grams  of  water  vapor  in  the  amounts 
of  these  gases  in  the  air  in  different  periods  of  the  day,  as,  for  example, 
at  the  beginning  and  cessation  of  hard  muscular  work  ;  but  with  ap- 
proximately uniform  muscular  activity  for  the  whole  period  the  residual 
amounts  of  these  gases  are  almost  invariably  the  same  from  day  to  day 


68  A    RESPIRATION   CALORIMETER. 

at  the  end  of  each  experimental  day,  i.  c.,  7.  a.  m.,  after  an  eight- 
hour  sleep. 

On  the  other  hand,  in  the  case  of  oxygen  there  is  present  in  the  sys- 
tem from  the  very  beginning  not  far  from  1,000  liters  of  oxygen,  which 
store  can  be  drawn  upon  by  the  subject,  and,  indeed,  is  drawn  upon  to 
a  very  considerable  extent.  It  is  of  course  immaterial  to  the  subject 
whether  he  uses  oxygen  from  the  steel  cylinder  in  which  the  oxygen 
is  duly  weighed,  or  oxygen  from  the  large  store  in  the  residual  air. 
Obviously,  when  taken  from  this  second  source,  provision  must  be 
made  for  noting  the  amount  thus  used.  If,  furthermore,  we  are  to  ob- 
tain data  regarding  the  exact  quantities  of  carbon  dioxide  and  water 
vapor  used  in  short  periods,  the  fluctuations  in  the  amounts  of  these 
materials  in  the  air  current  must  likewise  be  determined,  and  our  analy- 
ses of  residual  air  should  include  determinations  of  water  and  carbon 
dioxide  as  well  as  oxygen. 

POSSIBILITY  OF  LEAKAGE. 

From  a  consideration  of  the  construction  of  the  whole  apparatus,  it 
is  seen  that  it  is  practically  impossible  for  carbon  dioxide  to  leak  into 
or  out  of  the  air-circuit ;  for  if  there  were  a  leak  into  the  system,  a 
very  large  number  of  liters  of  room  air  would  have  to  enter  to  affect 
materially  the  weight  of  carbon  dioxide,  inasmuch  as  there  are  only 
4  parts  of  carbon  dioxide  per  10,000  of  air.  Similarly,  a  very  con- 
siderable leakage  of  air  out  of  the  system  would  be  necessary  before 
any  noticeable  amount  of  carbon  dioxide  would  have  escaped.  With 
reference  to  the  water  vapor,  much  the  same  can  be  said,  although  the 
percentage  of  water  vapor  in  the  air  of  the  calorimeter  laboratory  is 
much  greater  than  the  percentage  of  carbon  dioxide.  There  is,  more- 
over, a  possibility  (although  in  all  of  our  experience  it  has  never  yet 
occurred)  that  water  from  the  cooling  current  of  water  used  to  bring 
away  the  heat  may  leak  into  the  system  through  the  connections  with 
the  heat-absorbers  (see  p.  123);  but,  for  all  practical  purposes,  we  may 
consider  that  the  construction  of  the  apparatus  is  such  as  to  make  it 
impossible  for  any  appreciable  amounts  of  carbon  dioxide  or  water 
vapor  to  leak  into  or  out  of  the  system. 

In  the  case  of  oxygen  and  nitrogen,  however,  it  is  of  fundamental 
importance  that  there  be  no  leakage  of  these  gases  into  or  out  of  the 
system.  The  precautions  taken  to  secure  thorough  closure  of  the  sys- 
tem have  already  been  discussed  in  considerable  detail.  The  residual 
analyses  give,  as  is  shown  on  page  88,  data  for  determining  any  gain 
or  loss  of  nitrogen  to  the  residual  air,  and  consequently,  as  a  leakage 
of  air  in  either  direction  would  result  in  a  marked  disturbance  of  the 
amount  of  nitrogen  remaining  in  the  chamber,  the  residual  analysis  is 


CALCULATION   OP   RESULTS.  69 

frequently  of  great  assistance  in  indicating  such  leakage.  Furthermore, 
the  residual  analysis  is  used  to  measure  the  amount  of  leak.  This  point, 
as  well  as  the  general  significance  of  leaks  of  either  oxygen  or  nitrogen, 
will  be  taken  up  more  in  detail  beyond. 

FACTORS  USED  IN  THE  CALCULATION  OF  THE  RESIDUAL  ANALYSES. 

The  chief  factors  necessary  in  the  calculations  of  the  residual  amounts 
of  carbon  dioxide,  water  vapor,  oxygen,  and  nitrogen  in  the  ventilating 
air  current  are  the  volumes  of  the  gases  in  the  various  parts  of  the  sys- 
tem, the  composition  of  the  different  portions  of  air,  the  volume  of  the 
sample  taken  for  analysis,  the  weights  of  carbon  dioxide  and  water  in 
the  sample  drawn  through  the  meter,  and  the  volume  percentage  of 
oxygen  and  nitrogen  found  by  the  gasometric  analysis. 

VOLUMES  OP   AIR  IN   AIR-CIRCUIT. 

The  volume  of  the  residual  air  in  the  different  parts  of  the  chamber, 
pipes,  absorbing  apparatus,  and  pans  is  calculated  with  considerable 
accuracy  from  measurements  of  dimension,  especially  for  those  parts  of 
the  system  in  which  the  air  volumes  are  not  liable  to  fluctuate. 

VOLUME  IN  CHAMBER. 

The  respiration  chamber  is  19.27  decimeters  high,  12.17  decimeters 
wide,  and  21.38  decimeters  long.  The  corners  of  the  floor  and  ceiling 
are  rounded,  the  radius  of  curvature  being  1.27  decimeters.  From 
these  data  the  volume  of  the  chamber  proper  is  computed  to  be  4,987.0 
liters.  A  recess  in  the  wall  provides  for  the  window,  and  as  this  does 
not  set  flush  with  the  inner  wall,  its  volume  must  be  added  to  that  of 
the  rest  of  the  chamber.  The  recess  is  7.24  decimeters  high,  5.20  deci- 
meters wide,  and  0.57  decimeter  deep.  Its  volume  consequently  equals 
21.4  liters,  which,  added  to  the  volume  of  the  chamber,  4,987.0  liters, 
equals  5,008.4  liters. 

A  certain  amount  of  material  in  the  apparatus  can  be  considered 
permanent  fixtures,  such  as  the  absorbing  system,  the  air-pipe  and 
metal  work  (other  than  the  metal  of  the  walls) ,  the  telephone  and  bat- 
teries, and  various  smaller  pieces  of  apparatus  that  are  in  regular  use. 
The  volume  occupied  by  these  permanent  fixtures  is  determined  by 
measurement  of  their  dimensions  or  by  calculating  the  volume  by 
means  of  the  specific  gravity  when  the  weight  is  known.  The  volumes 
thus  obtained  are  as  follows,  in  liters:  Heat-absorbing  system,  5.94;  air- 
pipes  and  metal  work,  i.o;  switch,  0.3  ;  telephone  and  battery,  2.0  ; 
making  a  total  of  9.24  liters  to  be  deducted  from  the  apparent  volume, 
5,008.4  liters,  in  all  calculations. 


70  A   RESPIRATION   CALORIMETER. 

VOLUME    OF    AIR    IN    THE    AIR-PIPE    FROM  THE    CHAMBER,    MERCURY   VALVES, 

AND  BLOWER. 

The  ventilating  air-pipes  consist  of  ordinary  iron  gas-pipe  galvanized 
inside  and  out,  and  vary  considerably  in  length  as  well  as  diameter. 
From  measurements  of  the  length  and  internal  diameter  their  volume 
was  computed,  as  were  also  the  volumes  of  the  accessory  members  of 
the  air  system,  such  as  the  blower,  mercury  valves,  and  rubber  con- 
nections. From  these  data  it  is  calculated  that  the  air  between  the 
chamber  and  the  level  of  the  acid  in  the  first  water- absorber  occupies 
a  volume  of  6.55  liters. 

VOLUME  OF  AIR  IN  WATER-ABSORBERS. 

The  content  of  the  water-absorbers  was  estimated  by  filling  them 
to  the  top  of  the  exit  tube  with  water  and  noting  the  amount  required. 
For  one  absorber  this  was  found  to  be  14.38  liters,  for  the  other  14.69 
liters,  or  an  average  of  14.54  liters.  The  rubber  tubes  which  serve  to 
connect  the  absorbers  increase  the  volume  to  15.16  liters  each.  Of  this, 
0.93  liter  is  contained  in  the  entrance  tube  reaching  to  the  bottom  of 
the  absorber,  or  14.23  liters  for  the  remainder  of  the  absorber. 

From  this  figure  must  be  deducted  the  volume  occupied  by  the  sul- 
phuric acid.  This  is  originally  3  liters,  leaving  as  the  air  volume  1 1.23 
liters. 

VOLUME  OF  AIR  IN   CARBON-DIOXIDE  ABSORBERS. 

The  volume  of  air  in  the  soda-lime  cylinders  was  calculated  by  obser- 
vations upon  the  contraction  in  the  volume  of  air  under  a  known  press- 
ure. Three  soda-lime  cylinders  were  connected  in  series  in  the  usual 
way.  In  one  end  of  the  system  a  water  manometer  was  placed  and  the 
other  end  connected  with  a  bottle,  the  volume  of  which  was  determined 
by  weighing  it  when  empty  and  when  full  of  water.  When  a  known 
amount  of  water  was  poured  into  the  bottle  through  a  long  funnel-tube, 
the  air  in  the  bottle  and  in  the  three  absorbers  became  compressed,  the 
pressure  being  measured  by  the  manometer.  From  the  volume  of 
water  poured  into  the  bottle,  the  reading  on  the  manometer,  and  the 
barometric  pressure,  the  volume  of  air  in  the  system  could  be  calculated. 
Inasmuch  as  the  experiments  were  all  made  in  a  very  few  minutes,  no 
difference  in  temperature  was  taken  into  consideration  in  the  calcu- 
lations. 

From  three  determinations,  in  which  varying  quantities  of  water 
were  used,  the  total  volume  of  air  in  the  three  absorbers  varied  from 
10.128  to  10.486  liters,  averaging  10.28  liters  as  the  volume  of  air  in 
the  three  soda-lime  cylinders.  Since  the  apparatus  for  the  absorption 


CALCULATION   OF   RESULTS.  JI 

of  carbon  dioxide  includes  a  water-absorber  in  addition  to  the  three  soda- 
lime  cylinders,  the  volume  of  air  in  this  absorber  and  connections,  i.  <?., 
14.60  liters,  must  be  taken  into  consideration. 

VOLUME  OF  REMAINDER  OF  AIR  SYSTEM. 

The  volumes  of  the  mercury  valves  at  the  exit  end  of  the  absorbing 
system  and  the  pipes  back  to  the  calorimeter  are  computed  as  before. 
This  volume  is  equal  to  41.08  liters.  The  volume  of  the  pans  is  a 
fluctuating  one,  and  consequently  considered  under  the  head  of  fluctu- 
ating volumes. 

VOLUME  OF  OBJECTS   IN  THE  CHAMBER   NOT  PERMANENT. 

The  apparent  volume  of  air  in  the  respiration  chamber  (p.  69)  of 
5,008.4  liters  is  diminished  by  the  volume  of  the  objects  in  the  calo- 
rimeter. This  may  affect  the  calculation  of  results  in  two  ways.  In 
the  first  place,  the  total  volume  of  air  in  the  system  is  diminished  by 
the  presence  of  articles  inside  the  calorimeter  chamber.  In  an  alcohol 
check  experiment  (see  p.  96)  this  reduction  in  volume  of  the  air  is  a 
constant  one,  there  being  no  change  from  the  beginning  to  the  end  of 
the  experiment,  since  neither  the  window  nor  the  food  aperture  is 
opened  during  that  time,  and  the  volume  of  alcohol  inside  is  the  same 
at  the  beginning  and  the  end  of  each  experimental  period.  Under  such 
conditions,  therefore,  the  only  influence  of  the  presence  of  material 
inside  the  chamber  is  that  of  diminishing  the  apparent  volume  of  air. 
When  a  metabolism  experiment  with  man  is  in  progress,  however,  there 
may  be  very  material  differences  in  the  apparent  volume  of  air  in  the 
system,  due  to  the  fact  that  the  quantity  of  material  in  the  chamber  is 
constantly  varying  by  passage  into  or  out  of  the  food  aperture.  (See  p. 
75.)  Under  these  conditions  a  second  influence  may  be  exerted  by 
the  presence  of  material  inside  the  chamber,  i.  e.y  a  fluctuation  in  the 
actual  volume  of  gas  present. 

VOLUME  IN  AN  ALCOHOL  CHECK  EXPERIMENT. 

In  alcohol  check  experiments,  the  volume  of  the  air  in  the  chamber 
is  increased  as  the  inner  door  of  the  food  aperture  remains  open,  thus 
adding  4.63  liters  of  air,  the  volume  of  the  food  aperture,  to  the  system. 
In  addition  to  the  volume  of  the  permanent  fixtures,  9.24  liters,  it  is 
necessary  to  deduct  the  following  volumes,  in  liters  :  Lamp,  o.  2  (see  fig. 
22)  ;  alcohol  in  lamp,  0.4  ;  three  iron  stands  for  holding  the  lamp  and 
mirror,  0.95 — a  total  of  1.55  liters.  The  total  volume  of  air  in  the  sys- 
tem under  these  conditions  is  therefore  5,008.4  -f-  4.63 —  (1.55  +  9.24) 
=  5,002.24  liters. 


72  A   RESPIRATION   CALORIMETER. 

It  frequently  happens  that  other  fixtures,  such  as  the  metal  bed,  are 
left  in  the  chamber  when  making  the  alcohol  check  experiments. 
Under  these  conditions,  their  volumes  also  must  be  deducted. 

VOLUME  IN   EXPERIMENTS  WITH  MAN. 

In  metabolism  experiments  with  man,  the  alcohol  lamp  and  iron 
stands  are  removed.  The  food  aperture  is  closed,  and  consequently  its 
volume  is  not  added  to  that  of  the  chamber.  A  number  of  additional 
articles  are,  however,  taken  into  the  chamber  before  the  experiment 
begins.  Among  these  may  be  enumerated  the  bed,  table,  chair,  bed- 
ding, weighing  fixtures,  books,  papers,  dishes,  urine  jars,  feces  cans, 
and,  in  work  experiments,  the  ergometer.  By  far  the  greatest  correc- 
tion, however,  is  that  for  the  volume  of  the  subject  himself. 

The  specific  gravity  of  the  body  is  not  far  from  i.oo,  and  we  have 
been  in  the  custom  of  assuming  that  the  weight  of  the  subject  and 
clothing  represented  the  volume  in  liters  displaced  by  the  man  when 
entering  the  calorimeter  chamber.  The  corrections  for  the  furniture 
are  computed  by  means  of  the  weight  and  specific  gravity  of  the  vari- 
ous materials.  These  volumes  are,  in  liters,  as  follows  :  Bed,  3.66  ; 
table,  0.51  ;  chair,  with  weighing  attachments,  5.61,  and  ergometer, 
when  included,  14.00. 

A  similar  procedure  is  followed  in  the  calculation  of  volumes  of 
books,  papers,  and  incidental  articles. 

FLUCTUATIONS  IN  THE  AIR  VOLUME. 

While  the  apparent  volumes  of  air  in  the  different  sections  of  the 
closed  system  are  those  given  in  the  preceding  calculations,  there  are 
several  fluctuating  factors  that  must  be  taken  into  consideration. 

VOLUME  IN  THE  PANS. 

The  most  noticeable  and  important  fluctuation  in  volume  is  that 
specially  provided  for  in  the  construction  of  the  pans.  Sudden  fluctua- 
tions in  temperature  are  not  uncommon,  especially  in  the  change  from 
rest  to  hard  work,  or  vice  versa,  and  as  the  air  in  the  chamber  can  be 
considered  as  comparable  to  that  in  the  bulb  of  an  immense  air  ther- 
mometer, some  provision  for  expansion  or  contraction  must  be  made 
if  the  pressure  is  to  remain  constant.  Furthermore,  variations  in  baro- 
metric pressure  are  accompanied  by  very  material  alterations  in  the 
volume  of  the  confined  air. 

As  was  pointed  out  on  page  41,  fluctuations  in  the  volume  of  the  air 
in  the  pans  can  be  determined  with  considerable  accuracy  from  readings 
on  the  millimeter  scale  and  the  corresponding  table  of  calibrations. 


CALCULATION   OF   RESUI/TS.  73 

COMPRESSION  Of  AIR  IN   ABSORBING  SYSTEM. 

A  second  fluctuation  in  volume  is  due  to  the  fact  that,  as  air  is  forced 
through  the  absorbing  system,  the  increased  pressure  required  causes 
portions  of  the  air  to  be  somewhat  compressed.  The  chief  resistance 
to  the  passage  of  the  air  is  furnished  by  the  layer  of  sulphuric  acid  in 
the  two  water-absorbers.  When  the  acid  in  the  absorbers  is  fresh, 
i.  e.,  when  3.5  kilos  of  acid  of  the  specific  gravity  of  1.84  is  in  each, 
the  pressure  is  not  far  from  35  mm.  of  mercury.  The  resistance  of  the 
soda  lime  in  the  carbon-dioxide  absorbers  to  the  passage  of  the  air  has 
been  found  by  actual  experiment  to  be  relatively  insignificant. 

The  actual  measurement  of  air  in  the  system  is  made,  however,  at 
the  period  of  changing  from  one  absorbing  system  to  the  other,  i.  <?., 
at  the  end  of  each  experimental  period.  Under  these  conditions,  there- 
fore, since  the  air  in  all  other  parts  of  the  circulating  system  is  at 
atmospheric  pressure,  we  have  to  do  only  with  the  air  in  the  first  water- 
absorber  and  the  three  carbon-dioxide  absorbers.  When  the  blower  is 
stopped  the  compressed  air  leaks  back  through  the  blower  into  the 
system,  and  the  pressure  on  that  portion  of  the  air  confined  between 
the  blower  and  the  level  of  the  sulphuric  acid  in  the  entrance  pipe  of 
the  first  water- absorber  becomes  atmospheric.  Since  the  exhaust  tube 
from  the  last  water- absorber  connects  directly  through  the  main  air- pipe 
to  the  chamber,  the  air  above  the  acid  in  this  absorber  is  likewise  at 
atmospheric  pressure.  The  air  above  the  sulphuric  acid  in  the  first 
water-absorber,  as  well  as  the  air  in  the  three  carbon-dioxide  absorbers 
and  that  small  portion  confined  in  the  entrance  pipe  of  the  last  water- 
absorber,  remains,  however,  under  a  somewhat  increased  pressure. 
Consequently,  in  order  to  obtain  the  true  volume  of  air  in  that  portion 
of  the  absorbing  system  under  increased  pressure,  it  was  formerly  nec- 
essary to  correct  the  volume  for  the  increased  pressure.  By  a  simple 
process  of  calculation  it  was  found  that  the  difference  in  the  volume  of 
the  air  confined  in  this  portion  of  the  absorber  system  at  atmospheric 
pressure  and  under  the  slightly  increased  pressure  amounted  to  not  far 
from  0.4  liter.  There  was  therefore  a  discharge  of  air  from  the  system 
as  a  whole  amounting  to  0.4  liter  every  time  the  absorbing  system  was 
changed. 

As  a  verification  of  the  calculations,  provision  was  made  to  allow 
the  compressed  air  to  escape  through  the  Elster  meter,  the  amount  es- 
caping being  thus  measured  accurately.  This  was  found  to  be  almost 
invariably  0.4  liter. 

In  the  more  recent  experiments,  when  the  plan  for  testing  the  ab- 
sorbing system  described  on  page  32  was  put  in  operation,  this  correc- 
tion for  the  air  contained  in  the  absorbers  at  the  end  of  this  period  has 


74  A    RESPIRATION   CALORIMETER. 

not  been  applied,  since,  in  the  very  process  of  testing,  the  air  in  the  first 
water- absorber  and  the  three  carbon-dioxide  absorbers  was  left  in  some- 
what compressed  form  after  the  test,  and  obviously  the  true  volume  of 
air  in  this  portion  of  the  system  was  the  same  at  the  beginning  as  at 
the  end  of  each  period. 

CORRECTION   FOR  MERCURY  VALVE. 

In  the  manipulation  of  the  mercury  valve1  at  the  end  of  each  exper- 
imental period,  a  certain  amount  of  air  is  rejected  from  the  system, 
since,  by  the  raising  of  the  mercury  reservoir,  air  in  the  annular  space 
is  forced  back  into  the  last  water- absorber,  and  when  this  is  uncoupled 
escapes  into  the  room  air.  The  volume  of  air  thus  rejected  has  been 
determined  very  accurately  to  be  0.13  liter,  and  this  is  a  constant 
correction  to  be  applied  for  every  period.  The  correction  is  applied 
on  the  blank  for  the  calculation  of  the  residual  amounts  of  nitrogen, 
oxygen,  carbon  dioxide,  and  water  vapor,  as  shown  on  page  84. 

INCREASE  IN  VOLUME  OF  THE  WATER-ABSORBERS. 

As  the  water  vapor  is  absorbed,  the  volume  of  the  acid  in  the  absorber 
gradually  increases,  and  consequently  the  volume  of  air  decreases.  As 
this  volume  of  air  is  practically  driven  into  the  air  system,  a  correction 
for  it  is  necessary.  The  specific  gravity  of  concentrated  sulphuric  acid 
is  1.84,  and  as  water  is  absorbed  the  specific  gravity  becomes  lower. 
There  is,  however,  a  contraction  in  volume  which  must  be  allowed  for 
in  the  calculations.  It  has  been  computed  that  approximately  0.7  of 
the  weight  of  the  water  absorbed  when  expressed  in  cubic  centimeters 
corresponds  to  the  increase  inside  the  water- absorbers,  and  consequently 
it  is  customary  to  multiply  the  number  of  grams  of  water  absorbed  by 
0.7,  the  product  equaling  the  volume  of  air  in  cubic  centimeters  forced 
out  of  the  water-absorbers.  This  correction  is  always  in  one  direction, 
and  hence  a  cumulative  one,  and,  though  small,  is  made.  On  the 
blank  in  which  the  data  for  the  weights  of  the  absorbing  system  are 
recorded,  the  amount  of  this  correction  is  calculated  by  multiplying  the 
weight  of  water  collected  in  the  first  water- absorber  by  0.7,  e.  g.,  as 
illustrated  on  page  64,  54.71  X  0.7  =  38.297  =  0.04  liter.  That  is  to 
say,  0.04  liter  of  air  was  expelled  from  the  water- absorber  during  this 
particular  period. 

FLUCTUATIONS  IN  VOLUME  OF  THE  CARBON-DIOXIDE  ABSORBERS. 

That  there  is  an  actual  difference  between  the  volumes  of  the  sodium 
hydroxide  and  calcium  hydroxide  at  the  beginning  and  those  of  the 
sodium  carbonate  and  calcium  carbonate  at  the  end  is  highly  probable, 

1For  construction  of  valve  and  diagram,  see  page  21. 


CALCULATION   OF   RESULTS.  75 

as  can  be  inferred  from  the  slight  difference  in  their  specific  gravities. 
The  effect  of  such  difference  would  be  to  drive  air  from  the  carbon- 
dioxide  absorbers  into  the  closed  circuit  by  virtue  of  the  increased 
volume  of  the  absorbent.  That  the  increase  in  volume  would  be  suffi- 
ciently large  to  affect  our  results  is,  however,  very  questionable,  and 
owing  to  the  lack  of  data  we  have  made  no  correction  for  it. 

In  addition  to  the  possible  difference  in  volumes  of  the  reagent  at 
the  beginning  and  end  of  the  period,  there  is  a  loss  of  water  from  the 
carbon-dioxide  absorbers  corresponding  to  the  amount  taken  up  by  the 
air  and  absorbed  by  the  last  water- absorber.  Inasmuch  as  the  quantity 
rarely  exceeds  50  grams  per  two- hour  period,  it  has  been  assumed  for 
purposes  of  calculation  that  it  is  the  equivalent  of  distilling  50  grams 
of  water  occupying  a  volume  of  50  cc.  from  the  three  carbon-dioxide 
absorbers  into  the  water- absorber,  where  the  50  cc.  become  reduced  in 
volume  by  the  contraction  taking  place  when  mixed  with  sulphuric  acid 
to  50  X  0.7  =  35  cc.  Thus,  even  in  maximum  cases,  there  is  a  difference 
in  volume  due  to  absorption  of  water  in  the  last  water-absorber  of  only 
15  cc.  In  the  work  so  far  this  amount  has  been  entirely  neglected. 

It  is  thus  seen  that  no  correction  is  applied  at  present  for  any  possible 
changes  in  the  air  volume  of  the  carbon-dioxide  absorbers. 

INTERCHANGE  OF  AIR  THROUGH   FOOD   APERTURE. 

The  double  door  on  the  food  aperture  (see  fig.  8)  makes  it  possible 
to  put  into  the  chamber  or  remove  from  the  chamber  food  and  excreta , 
and  the  vessels  in  which  they  are  contained,  without  causing  any  great 
change  in  the  air  admitted  to  or  removed  from  the  chamber  during  this 
process.  When  the  inner  door  is  closed  and  the  outer  door  is  open,  it  is 
assumed  that  the  air  in  the  food  aperture  has  the  composition  of  that  of 
the  laboratory.  On  the  other  hand,  when  the  outer  door  is  closed  and 
the  inner  door  open,  it  is  assumed  that  the  air  in  the  food  aperture 
has  the  composition  of  the  air  inside  of  the  chamber.  It  is  possible, 
however,  that  while  air  ordinarily  diffuses  quite  rapidly,  the  composi- 
tion of  air  in  the  food  aperture  does  not  change  as  rapidly  or  as  com- 
pletely as  the  above  assumptions  would  imply. 

We  have  assumed  that  laboratory  air  contains  20  per  cent  of  oxygen 
and  80  per  cent  of  nitrogen,  not  allowing  for  a  small  quantity  of  water 
vapor  and  carbon  dioxide.  The  composition  of  the  air  in  the  chamber 
is  always  very  different  from  that  of  the  air  in  the  laboratory,  the 
difference  being  most  pronounced  as  to  the  carbon  dioxide  present,  as 
this  may  be  anywhere  from  12  to  60  times  the  normal  amount.  The 
percentage  of  oxygen  is  in  general  lower  than  normal,  at  times  being 
as  low  as  17  per  cent,  though  ordinarily  it  is  not  far  from  19.5  to  20 


76  A   RESPIRATION   CALORIMETER. 

per  cent.  If  we  assume  for  an  average  percentage  of  air  inside  the 
chamber  19  per  cent  of  oxygen,  i  per  cent  of  carbon  dioxide,  and  80 
per  cent  of  nitrogen,  it  follows  that  every  time  the  food  aperture  is 
open  there  is  an  admission  of  oxygen  to  the  system  and  a  loss  of  carbon 
dioxide,  with  no  very  great  change  in  the  amount  of  nitrogen.  The 
actual  variations  in  the  amounts  thus  admitted  and  removed  have  as  yet 
not  been  taken  into  consideration,  though  during  heavy-work  experi- 
ments, when  as  much  as  0.04  gram  of  carbon  dioxide  is  collected  in  the 
lo-liter  air  sample  used  for  residual  analysis,  as  much  as  0.02  gram  of 
carbon  dioxide  may  be  lost  from  the  system  every  time  the  food  aperture 
is  open.  In  experiments  it  is  sometimes  opened  as  often  as  20  times 
per  day,  and  it  is  thus  seen  that  under  these  circumstances  a  not  incon- 
siderable amount  of  carbon  dioxide  may  be  lost  from  the  system .  The 
amount  of  oxygen  thus  admitted  is  of  less  consequence,  though  the 
desirability  of  certainty  as  to  its  amount  would  suggest  that  more  atten- 
tion might  be  paid  to  this  correction. 

Another  important  correction  in  connection  with  the  opening  and 
closing  of  the  food  aperture  is  the  displacement  of  air  by  the  various 
articles  of  food,  excreta,  and  dishes  passed  into  and  out  of  the  chamber. 
If  we  consider  the  volume  of  air  in  the  respiration  chamber  as  5,000 
liters,  then  obviously,  if  a  liter  of  water  or  metal  or  glass  is  passed  into 
the  food  aperture,  the  total  volume  of  air  is  reduced  to  4,999  liters.  On 
the  contrary,  if  a  liter  of  urine  or  of  drip  water  or  a  volume  of  glass 
and  metal  equivalent  to  i  liter  is  passed  out  of  the  chamber,  the  volume 
of  air  is  increased  to  5,001  liters. 

It  is  therefore  of  considerable  importance  that  the  volume  of  this  in- 
terchange through  the  food  aperture  be  known,  not  merely  from  day 
to  day,  but  from  period  to  period.  To  aid  in  determining  this  inter- 
change, a  schedule  has  been  prepared,  the  so-called  "food  aperture 
sheet,"  in  which  entries  are  made  of  all  material  entering  and  leaving 
the  chamber.  On  this  sheet  are  recorded  the  time  at  which  the  food 
aperture  is  opened,  the  nature  and  weight  of  the  containers  and  their 
contents,  and  the  temperature  when  not  that  of  the  chamber. 

The  temperature  records  are  more  numerous  for  materials  entering 
the  chamber  than  for  those  leaving  it,  since  the  attempt  is  made  to  have 
all  articles  in  the  chamber  remain  there  until  they  have  acquired  the 
chamber  temperature. 

In  calculating  the  volume  of  air  displaced  by  the  different  materials 
entering  and  leaving  the  food  aperture,  it  is  necessary  to  take  into 
account  not  only  the  weight  but  also  the  specific  gravity.  For  the 
materials  entering  the  chamber,  i.  <?.,  the  food,  drink,  and  containers, 
the  following  specific  gravities  are  used  :  For  glass,  porcelain,  etc.,  2.6  ; 


CALCULATION   OF   RESULTS.  77 

for  sugar,  carbohydrates,  bread,  crackers,  cereals,  etc.,  1.5  ;  for  books, 
papers,  underclothes,  etc.,  i.o  ;  for  milk,  cream,  butter,  drinking  water, 
cereal  coffee,  beef  tea,  i  .o.  The  specific  gravity  of  both  urine  and  feces 
is  taken  as  i.o. 

The  calculations  of  volume  are  made  by  dividing  the  weight  of 
material  by  the  specific  gravity.  Thus,  inasmuch  as  the  interchange 
through  the  food  aperture  should  be  known  for  each  experimental 
period,  it  is  our  custom  to  add  together  the  weights  of  all  the  glass 
entering  the  food  aperture  during  the  period  in  question  and  then 
divide  the  total  weight  by  the  specific  gravity,  2.6.  In  a  similar  man- 
ner the  total  weight  of  sugar,  carbohydrates,  bread,  cereals,  etc. ,  is  found 
and  this  value  divided  by  the  specific  gravity,  1.5.  The  volume  of  the 
materials  leaving  the  respiration  chamber  during  this  same  experimental 
period  is  likewise  found,  and  the  difference  between  the  two  volumes, 
i.  e. ,  the  volume  of  the  material  entering  the  chamber  and  the  volume 
of  the  material  leaving  the  chamber,  is  taken  as  representing  the  volume 
of  air  either  removed  from  or  added  to  the  air  in  the  closed  circuit.  If 
the  volume  of  material  entering  the  chamber  is  larger  than  the  volume 
of  material  leaving  it,  this  difference  in  volume  is  subtracted  from  the 
air  in  the  system,  and  if,  on  the  other  hand,  the  volume  of  material 
leaving  the  chamber  is  greater  than  that  entering  the  chamber,  the 
volume  of  air  equivalent  to  this  difference  is  added  to  the  total  volume 
of  air  in  the  system.  This  correction  in  volume  is  made  for  every  ex- 
perimental period.  (See  blank  on  p.  84.) 

.ADDITION  OF  NITROGEN  WITH  THE  OXYGEN. 

As  oxygen  is  admitted  to  the  system,  there  is  a  continuous  addition 
of  nitrogen  which  accumulates  in  the  ventilating  air-circuit.  The 
amount  thus  admitted  is  calculated  very  exactly,  as  has  been  shown  on 
page  34.  The  application  of  this  correction  in  the  volumes  will  be 
discussed  when  the  total  amount  of  nitrogen  in  the  system  is  considered. 
(See  p.  88.) 

THE  REJECTION  OF   AIR. 

Since  the  amount  of  nitrogen  in  the  closed  air-circuit  accumulates 
as  a  result  of  its  admission  as  an  impurity  in  the  oxygen,  it  becomes 
necessary  to  reject  air  from  time  to  time,  replacing  it  with  pure  oxygen, 
i.  e.,  oxygen  containing  from  2.5  to  8  per  cent  nitrogen,  to  keep  up 
the  normal  percentage  of  oxygen  in  the  main  air  current.  In  order  to 
know  exactly  the  proportions  of  oxygen  and  nitrogen  rejected,  it  is 
desirable,  theoretically  at  least,  to  make  an  analysis  of  a  sample  of  the 
air  rejected.  In  practice,  however,  we  have  been  in  the  habit  of  re- 


78  A   RESPIRATION   CALORIMETER. 

jecting  when  necessary  a  considerable  quantity  of  air  (30  to  70  liters) 
immediately  after  the  beginning  of  the  experimental  period  at  7  a.  m., 
thereby  making  use  of  the  data  obtained  from  the  analysis  of  the  air 
at  7  a.  m.  in  determining  the  composition  and  amount  of  the  oxygen 
and  nitrogen  rejected. 

Under  these  conditions  the  analysis  of  air  at  7  a.  m.  holds  good  for 
the  first  portion  of  air  rejected,  but,  in  order  to  keep  up  the  normal 
volume  of  air  in  the  system  and  thus  not  draw  the  rubber  diaphragms 
on  the  pans  down  too  tightly,  it  soon  becomes  necessary  to  admit  oxygen 
into  the  main  air-pipe  and  thereby  alter  the  composition.  To  delay 
this  step  as  much  as  possible,  and  so  diminish  its  effect  on  the  compo- 
sition of  the  air  rejected,  we  allow  the  temperature  inside  the  chamber 
to  rise  somewhat,  as  is  its  tendency  when  the  subject  is  moving  around 
vigorously,  as  at  this  time  of  day,  and  thus  utilize  the  expansion  of  the 
air  to  keep  the  pans  partially  filled  even  when  considerable  air  is  being 
rejected.  Under  these  conditions,  while  it  is  probably  true  that  the  per- 
centage of  oxygen  in  the  last  portion  of  the  air  rejected  is  somewhat 
higher  than  that  in  the  first  portion,  we  have  customarily  assumed 
that  the  analysis  of  air  at  7  o'clock  represents  so  nearly  the  actual 
composition  of  the  air  that  no  correction  is  necessary. 

In  rejecting  air,  the  petcock  on  the  entrance  pipe  of  the  Elster 
meter,  through  which  the  air  sample  is  usually  drawn,  is  closed,  and  the 
petcock  connecting  the  entrance  pipe  of  the  meter  with  the  main  air- 
pipe  at  a  point  between  the  pans  and  the  inlet  for  oxygen  is  opened. 
The  screw  pinchcock  on  the  T  tube,  through  which  the  air  sample  for 
oxygen  analysis  is  taken,  is  opened,  thus  permitting  free  exit  of  the 
air  leaving  the  suction-pump.  The  air  is  rejected  as  soon  as  possible 
after  the  end  of  the  second  residual  analysis.  Inasmuch  as  there  is 
but  little  resistance  between  the  main  air-pipe  and  the  meter,  the  gas 
passes  through  the  meter  very  rapidly,  and  consequently  50  to  60  liters 
of  air  can  be  rejected  in  about  15  minutes.  The  manometer  indicates 
a  slightly  diminished  pressure,  amounting  to  not  far  from  20  mm.  of 
water,  which,  together  with  the  temperature  of  the  meter,  is  read 
when  half  the  air  is  rejected. 

From  the  volume  of  air  as  measured  by  the  meter,  the  temperature 
of  the  meter,  the  manometer  reading,  and  the  barometric  pressure,  it 
is  possible  to  calculate  exactly  the  volume  and  weight  of  oxygen  and 
nitrogen  rejected. 

Occasionally,  especially  when  a  sudden  fall  in  barometric  pressure 
has,  by  virtue  of  the  expansion  of  the  gases  in  the  closed  system,  so 
retarded  the  admission  of  oxygen  that  the  percentage  of  oxygen  has 
fallen  considerably  below  normal,  it  has  been  necessary  to  reject  air 


CALCULATION  OP   RESULTS.  79 

at  other  hours  of  the  day  than  at  7  a.  m.  Under  these  conditions  it  is 
customary  to  make  an  analysis  of  a  sample  taken  in  the  middle  of  the 
process  of  rejection. 

Since  the  air  is  rejected  after  it  has  left  the  absorbing  system,  it  is 
assumed  that  it  is  free  from  carbon  dioxide  and  water  vapor.  Save  in 
very  rare  instances  in  which  large  quantities  of  carbon  dioxide  are  being 
absorbed  by  the  soda  lime  and  the  cylinders  have  become  very  much 
heated  as  a  result  of  the  absorption,  we  have  never  found  carbon  diox- 
ide in  the  air  current  leaving  the  absorbers.  The  efficiency  of  the  last 
water-absorber,  provided  it  has  not  gained  in  weight  over  400  grams,  is 
such  as  to  preclude  the  possibility  of  the  presence  of  any  weighable 
amount  of  water.  It  is  therefore  assumed  that  nothing  but  nitrogen 
and  oxygen  are  rejected,  no  account  being  taken  of  the  possible  pres- 
ence of  argon  or  other  gases  not  absorbed  by  potassium  pyrogallate, 
sulphuric  acid,  and  soda  lime.  The  small  quantities  of  marsh  gas 
resulting  from  putrefactive  changes  in  the  intestinal  tract  have  also 
been  disregarded.  That  these  are  considerable  in  man  is  not  at  all 
well  established. 

RESPIRATORY  I,OSS. 

As  the  food  is  eaten,  digested,  and  oxidized,  i.  e.,  converted  into 
gaseous  products,  the  volume  of  solids  in  the  chamber  is  constantly 
diminished  and  the  volume  of  gas  increased.  In  a  similar  manner,  if, 
in  a  fasting  experiment,  the  subject  draws  upon  his  body  material,  it 
is  assumed  that  the  volume  of  his  body  is  diminished.  These  fluctua- 
tions have  been  a  rather  elusive  object  of  search.  Perhaps  the  most 
accurate  estimate  is  obtained  by  adding  together  for  each  period  the 
weight  of  water  vaporized  and  of  carbon  dioxide  eliminated  and  sub- 
tracting from  it  the  weight  of  oxygen  consumed.  This  figure,  here 
termed  the  "respiratory  loss,"  represents  what  the  subject  loses  in 
weight  during  the  period,  exclusive  of  the  water  which  may  have  been 
vaporized  in  perspiration  and  recondensed  on  the  heat-absorbers  inside. 
No  account  of  this  is  taken,  since  in  all  probability  it  occupies  the 
same  volume  in  the  absorbers  that  it  did  within  the  subject.  This 
respiratory  loss  gives  an  estimate  of  the  amount  of  substance  changed 
from  solids  to  gas  during  a  given  period.  It  is  assumed  that  each  gram 
of  material  occupied  i  cc.  and  the  volume  of  air  in  the  chamber  should 
be  increased  by  this  amount  in  calculating  the  residual  amount  at  the 
end  of  each  period. 

As  a  matter  of  fact,  in  the  calculations  of  the  last  few  experiments, 
instead  of  using  the  weight  of  the  total  amount  of  carbon  dioxide 
eliminated  during  a  given  period,  we  have  used  the  value  obtained  by 


80  A    RESPIRATION   CALORIMETER. 

weighing  the  carbon-dioxide  absorbers.  No  notice  was  therefore  taken 
of  the  change  in  the  amount  of  residual  carbon  dioxide.  Theoret- 
ically, of  course,  this  should  be  taken  into  consideration,  although  the 
ultimate  result  in  24  hours  is  compensating  and  no  error  finally  results. 
In  the  first  morning  period,  i,  e.,  from  7  a.  m.  to  9  a.  m.,  the  amount 
of  carbon  dioxide  collected  in  the  absorbers,  especially  in  a  work  ex- 
periment, is  considerably  less  than  that  actually  eliminated.  On  the 
other  hand,  in  the  later  periods  of  the  day  the  amount  of  carbon 
dioxide  thus  absorbed  is  more  than  that  actually  eliminated  during  a 
given  period. 

A  similar  criticism  applies  to  the  use  without  correction  of  the 
weight  of  oxygen  admitted  for  the  variations  in  the  residual  amount 
of  oxygen.  As  regards  water  vapor,  no  changes  in  residual  amounts 
that  could  materially  affect  this  calculation  are  possible. 

In  general,  however,  the  actual  correction  for  respiratory  loss  is  not 
very  large,  and,  while  the  residual  amounts  of  carbon  dioxide  and 
oxygen  should  theoretically  be  taken  into  consideration  in  the  cal- 
culation, it  would  be  rather  difficult  and  somewhat  costly  to  carry 
through  a  preliminary  calculation  to  determine  the  total  amount  of 
residual  carbon  dioxide  and  then  recalculate  the  experiment,  allowing 
exactly  for  the  respiratory  loss. 

SUBDIVISION  OF  AIR  VOLUMES. 

In  calculating  the  true  volume  of  gases  in  the  different  parts  of  the 
system,  it  is  necessary  to  take  into  consideration  the  apparent  volume  as 
shown  in  the  preceding  section  of  this  report,  the  barometric  pressure, 
and  the  temperature.  Of  these  three  factors,  the  apparent  volumes 
are  determined  by  measurement,  and  the  barometric  pressure  is  that 
of  the  atmosphere,  since  the  volumes  of  gas  are  measured  when  the 
blower  is  stopped,  and  due  corrections  are  made  for  that  small  propor- 
tion of  the  total  air  which  is  confined  in  the  first  water-absorber  and 
the  carbon-dioxide  absorbers.  The  temperature  measurements  are 
made  in  two  places — first,  that  of  the  large  volume  of  air  in  the  res- 
piration chamber,  and  second,  that  of  the  exterior  portions  of  the 
apparatus.  For  calculating  the  true  volume  of  air,  four  subdivisions 
of  the  air  volume  are  made  on  the  basis  of  differences  in  composition 
or  temperature  as  follows  : 

I.  The  volume  of  air  in  the  chamber. 

II.  The  air  in  the  pipe  from  the  chamber  to  the  absorbing  system, 
including  the  blower  and  the  entrance  pipe  of  the  first  water-absorber. 

III.  The  volume  of  air  from  the  bottom  of  the  first  water-absorber 
to  the  entrance  end  of  the  second  carbon-dioxide  absorber. 


CALCULATION   OP   RESULTS.  8 1 

IV.  The  volume  of  air  in  the  remaining  carbon-dioxide  absorbers, 
second  water- absorber,  and  pipe  from  the  absorber  back  to  the  chamber. 
To  this  is  also  added  the  fluctuating  volume  of  the  air  in  the  pans. 

Volume  I  is  measured  at  T0,  the  temperature  of  the  chamber  ;  volumes 
II,  III,  and  IV  are  measured  at  T,  the  temperature  registered  by  a 
mercury  thermometer  near  the  pans. 

As  a  result  of  the  removal  of  carbon  dioxide  and  water  vapor  and 
the  admission  of  oxygen,  the  air  in  the  different  parts  of  the  air-circuit 
is  of  varying  composition,  and  consequently,  in  any  calculation  in 
which  the  total  residual  amounts  of  carbon  dioxide,  water  vapor, 
oxygen,  and  nitrogen  are  to  be  determined,  the  composition  of  the 
different  parts  must  be  taken  into  consideration. 

It  is  assumed  that  all  the  water  vapor  in  the  air  current  is  absorbed 
by  the  first  water-absorber  during  the  passage  of  the  air  current  through 
the  acid,  so  that  there  is  no  moisture  in  the  air  above  the  acid  in  the 
water-absorber.  It  is  further  assumed  that,  in  general,  by  the  time 
the  air  current  has  passed  through  the  first  carbon-dioxide  absorber 
its  carbon-dioxide  content  has  been  reduced  to  zero.  A  second  sub- 
division may  therefore  be  made  of  the  air  volumes,  based  solely  upon 
the  variations  in  composition  of  different  parts  of  the  system. 

The  first  two  sections  of  the  subdivision  outlined  above,  i.  <?.,  I  and 
II,  are  alike,  save  as  regards  the  temperature  measurements.  They 
differ  from  sections  III  and  IV  in  that  they  contain  water  vapor  in 
addition  to  the  carbon  dioxide,  oxygen,  and  nitrogen.  The  volume  of 
air  containing  water  vapor,  therefore,  is  the  sum  of  I  and  II,  and 
may  be  designated  Vj.  The  air  in  the  third  section  above,  i.  e.,  Ill, 
though  free  from  water,  contains  carbon  dioxide  in  addition  to  oxygen 
and  nitrogen,  and  consequently  the  total  volume  of  air  containing 
carbon  dioxide  is  I-fII+III.  This  volume  is  designated  as  V2.  The 
sum  of  the  four  subdivisions  obviously  includes  the  total  volume  of 
air  in  the  system,  and  represents  the  volume  of  carbon  dioxide,  water 
vapor,  oxygen,  and  nitrogen.  This  is  designated  as  V3. 

COMPOSITION   GRADIENT  OF  AIR  IN   CI.OSED  CIRCUIT. 

In  the  preceding  discussion  it  is  assumed  that  the  air  in  the  various 
sections  of  the  air-circuit  has  a  uniform  composition  in  each  individual 
section. 

Considering  the  closed  volume  of  air  absolutely  independent  of  the 
room  air,  as  is  the  case,  barring  leakage,  it  is  apparent  that  the  air  in  the 
respiration  chamber  proper  and  in  the  outgoing  air-pipe,  up  to  the 
time  that  it  first  comes  in  contact  with  the  acid  in  the  first  water- 
absorber,  contains  nitrogen,  oxygen,  carbon  dioxide,  and  water  vapor. 

6B 


82  A   RESPIRATION   CALORIMETER. 

The  air  entering  the  respiration  chamber  is  free  from  carbon  dioxide 
and  water,  and  contains  a  larger  percentage  of  oxygen  than  that  in  the 
chamber  itself.  Theoretically,  therefore,  there  will  be  a  space  about 
the  tube  conducting  air  into  the  chamber  that  will  have  varying  pro- 
portions of  the  different  constituents  ;  practically,  however,  the  slight 
differences  at  this  point  are  neglected. 

The  distribution  of  the  water  vapor  in  the  chamber  is  very  uneven, 
for  we  have  the  moist  surface  of  the  skin  of  the  subject  and  the  very 
moist  absorbing  system  in  the  upper  part  of  the  chamber,  and  conse- 
quently, with  the  tendency  of  moist  air  to  rise,  probably  the  upper 
half  of  the  air  in  the  chamber  contains  a  greater  amount  of  water  than 
the  lower  half.  That  this  difference  in  composition  is  sufficient  to 
affect  the  results  of  experiments  with  man  is  very  much  to  be  doubted, 
and  in  alcohol  check  experiments  the  rate  of  evolution  of  water  is  so 
slow  that  in  all  probability  natural  diffusion  produces  a  nearly  uniform 
moisture  content  throughout  the  whole  chamber.  In  all  these  calcu- 
lations, therefore,  it  is  assumed  that  each  portion  of  air  is  of  uniform 
composition. 

DA.TA  USED  IN  CALCULATING    RELATION  OF  WEIGHTS  AND  VOLUMES  OF  GASES. 

The  atomic  weights  of  hydrogen  and  oxygen  employed  in  these 
computations  are  those  derived  by  Morley,1  as  follows  :  Oxygen  =  16; 
hydrogen  =  1.00762.  According  to  the  same  authority,  the  weight  of 
i  liter  of  oxygen  at  45°  latitude  is  1.42900  grams.  Corrected  for 
gravity,  this  becomes,  at  Middletown,  1.42853  grams.  From  these 
data  the  weight  of  i  liter  of  hydrogen  is  readily  computed  as  0.089964 
gram,  and  water  vapor  as  0.80423  gram. 

The  atomic  weight  used  for  carbon  is  that  given  by  Clarke2  as  12.001. 
The  weight  of  i  liter  of  carbon  dioxide  is  accordingly  1.96427  grams. 

For  the  weights  of  a  liter  of  nitrogen  and  air,  data  given  by  three 
observers,  Von  Jolly,  Leduc,  and  Rayleigh,3  for  the  weight  of  a  liter  of 
oxygen  and  nitrogen  have  been  averaged.  In  this  way  the  weight  of  i 
liter  of  nitrogen  at  Middletown  has  been  computed  as  1.25668  grams. 
Similarly  the  weight  of  a  liter  of  dry  air,  which,  according  to  Rayleigh 
and  Ramsey,3  contains  20.91  per  cent  by  volume  of  oxygen  and  79.09 
per  cent  by  volume  of  nitrogen,  is  taken  as  1.29264  grams. 

The  figures  obtained  for  the  weight  of  i  liter  of  water  vapor  are  on 
the  assumption  that  it  is  a  perfect  gas  down  too0  and  obeys  the  law  of 
expansion  and  contraction  due  to  pressure  and  temperature.     Accord- 
Smithsonian  Contributions  to  Knowledge  (1895),  980,  p.  109. 
2  Smithsonian  Misc.  Coll.  (1882),  27,  p.  56. 
1  Smithsonian  Contributions  to  Knowledge  (1896),  1033,  p.  14. 


OF   RESULTS.  83 

ing  to  Hirn,  this  is  not  strictly  true.  The  coefficient  of  thermal  expan- 
sion of  perfect  gases  is  taken  as  0.00367,  whereas  Hirn1  states  that  the 
coefficient  of  thermal  expansion  of  water  vapor  is  0.00419  between  o° 
and  119°,  the  value  seeming  to  diminish  as  the  temperature  rises  and 
increasing  numerically  for  lower  temperatures.  Perman,2  however, 
concludes  that  the  density  of  saturated  aqueous  vapor  is  probably  only 
very  slightly  (if  at  all)  above  normal  at  temperatures  up  to  90°,  and 
from  the  data  at  hand  it  seems  reasonable  to  assume  that  water  vapor 
at  20°  behaves  as  a  perfect  gas,  and  that  the  weights  of  a  liter  of 
hydrogen  and  water  vapor  are  directly  proportional  to  their  molecular 
weight. 

CALCULATIONS   OP   RESIDUAL  ANALYSIS. 

In  calculating  the  total  amounts  of  carbon  dioxide,  water,  oxygen, 
and  nitrogen  in  the  residual  air  of  the  system  at  the  end  of  any  given 
period,  the  volumes  of  the  sample  and  the  apparent  volume  of  the 
whole  air  system  are  reduced  to  the  same  basis,  i.  e.,  the  standard  con- 
ditions at  o°  and  760  mm.  pressure,  thus  simplifying  the  calculations 
greatly. 

Reference  has  already  been  made  to  the  process  by  which  the  residual 
samples  are  taken,  and  specimen  data  for  such  samples  are  shown  in 
the  upper  left-hand  corner  of  the  record  sheet  previously  explained 
(p.  64).  There  remain  for  consideration,  first,  the  calculation  of  the 
true  volume  of  gas  in  the  sample  and  in  the  system,  and  second,  from 
these  corrected  data  the  calculation  of  the  amount  of  the  various  gases 
in  the  system. 

These  calculations  are  simplified  as  much  as  possible,  and  for  con- 
venience are  recorded  on  a  blank  shown  on  page  84. 

VOLUME  OF  THE  SAMPLE. 

The  calculation  for  the  samples  for  the  residual  analyses  involves  a 
reduction  of  the  gas  volume  as  measured  by  the  meter  to  standard  con- 
ditions of  temperature  and  pressure,  making  a  due  allowance  for  the 
volume  of  water  vapor  and  carbon  dioxide  absorbed  by  the  reagents, 
thus  giving  the  corrected  volume  of  air  withdrawn  in  the  samples  reduced 
to  standard  conditions.  The  calculations  for  the  reduction  of  these 
volumes  to  standard  conditions  is  made  on  the  residual  sheet  (p.  84). 
Under  the  head  ' '  Air  sample  for  analysis  ' '  is  first  entered  the  apparent 
volume  of  air  which  is  passed  through  the  meter.  To  the  logarithm 
of  this  volume  must  be  added  the  logarithm  of  the  calibration  correction 

1  Him  :  Recherches  sur  1'equivalent  mechanique  de  la  chaleur  (1858). 
2Proc.  Roy.  Soc.  (1904),  72,  pp.  72-83. 


84 


A   RESPIRATION   CALORIMETER. 


RESIDUAL  SHEET.  NO.  16. 

Calculation  of  the' Residual  Amounts  of  Nitrogen,  Oxygen,  Carbon  Dioxide,  and 
Water  Vapor  Remaining  in  Chamber  at  7  a.  m.,  April  9, 

Residual  at  end  of  I2th  period.     Metabolism  experim  ( nt  No.  77. 


Volumeofnitrogeninchamberats.ooa.m.       -        -       3574.14  liters. 
Nitrogen  in  air  sample  rejected  liters,  #N., 

OXYGEN  CORRECTIONS. 

Nitrogen  rejected  with  absorbers, 
Nitrogen  admitted  with  oxygen, 

No    interchange   through   food   aperture, 
out(-),     

Nitrogen  present  at  end  of  period, 

—  .10       " 

—  .04  grams. 

+  •54     " 

in    (+).    or 

3574.58     " 

AIR  SAMPLE  FOR  ANALYSIS. 

LOR.  10.016            -              1.  .00069 
Correction,           -         -         -9*895 
T   ,               ...         .96858 
Pressure       -                             -97992 

Manometer—   12.28  mm 
e  @  Tm,         —   17.84  mm 

Harometer  =  755.78  mm. 
Tm               —  20.44°C. 
Tc                 —  20.79°C. 
Tj                 —   20.0  °C. 

Sum               =—  30.12  mm 
Barometer  —755.78  mm 

.93814  —  8.672  1. 
Wt.  H20. 
.0554                                            74351 
Gms.  to  liters,       -         -       09*63 

Difference    =725.66  mm. 

APPARENT  VOLUME  OF  AIR. 

4909.88  -(-  .05 
—  4909.93!.  @Tc 
II.           —      6.55  1.  @  Tt 

83813—  .069  1. 
Wt.  CO» 
.0441                                            64444 
Gms.  to  liters,      -         -        7O68O 

Log.  —  94265 


351  24=    .022    1. 
^  =  8.763   1. 


III. 

«*-{£?} 


5,  14.60  — .04 


=     14.56  1.  ©  T! 
—    54.78  1.  @  TI 


Colog.  »0— 05735 


Pressure    - 
Log.  II.      - 

=  69107 
—  96806 
-       -       -99758 

LOST.  wt.  H2O  in  rt  sidual 
•0554           -       -       —     74351 
Log  V!       -       -       =     65729 
Colog.  v0                    —     05735 

458  :  5  =  28.72  gms. 
Gms.  to  liters       -           O9462 

H,0 

65671  —  4536.40!. 

—  81624 
—  969/4 

Pressure    - 


Log.  III. 

TI 

Pressure 


Log.  IV.  - 
TI  -  - 
Pressure  - 


Total  volume  of  air 
Volume  CO2  +  HaO 


0  +  N 
N 


78306= 


6.07  1. 
4542-47  I- 


•16316 
=  06924 
'99758 

12998=     13.49  1. 


4555-96  l-  —  v2 


=73862 
=96924 
=99758 

70544=     50.75  I- 

=  4606.71  1. 

-  -     47-381. 

-  -=4559-33  L 

3574  58  1. 

984.75 


1.  H20 


Log.  wt.  CO2  in  residual 


.0441 
Log.  V2 
Colog.  v0 


Gms.  to  liters 


Log.   984.75 
'     4559-33 


By  calculation 
By  analysis 


64444 
-  65858 
—  Q5735 

3  *  o  3  7  =  22.93  g*ns- 
70680 

(b)  o  6  7  i  7  =  1 1 .67  1.  CO» 

35-71      L 
11.67      L 

47.38  —  1. 


=  99333 
=  65890 

33443 


21.60% 
21.62  f 


CALCULATION   OP   RESULTS.  85 

for  the  Elster  meter  (see  p.  47),  the  cologarithm  of  the  correction 
corresponding  to  the  temperature  of  the  meter  Tm,  i.  e.,(i  +.00367 
Tm) ,  and  the  logarithm  corresponding  to  the  corrected  pressure.  The 
pressure  of  the  air  in  the  meter  during  the  process  of  taking  the  resid- 
ual sample  is  affected  by  three  factors — first,  the  atmospheric  pressure  ; 
second,  the  tension  of  aqueous  vapor  at  the  temperature  of  the  meter, 
and  third,  the  tension  of  the  air  on  the  meter  as  measured  by  the  water 
manometer.  By  referring  to  the  data  given  for  the  water  manometer 
on  the  blank  (p.  64),  it  is  found  that  in  this  instance  the  manometer 
when  reduced  to  millimeters  of  mercury  indicates  12.28  mm.  The 
temperature  of  the  meter  was  20.44°,  and  the  tension  of  aqueous  vapor 
at  this  temperature  indicated  in  the  calculations  by  e  equals  17.84  mm. 
The  sum  of  these  two  pressures  equals  30.12  mm.,  which  must  be  de- 
ducted from  the  barometric  pressure  to  give  the  corrected  pressure  on 
the  air  in  the  meter,  namely,  725.66  mm.  The  logarithmic  correction 
for  this  pressure,  i.  e.,  p~r-j6o,  is  .97992.  The  true  volume  of  air 
then  drawn  through  the  meter  is  8.672  liters.  This  does  not,  however, 
represent  the  total  volume  of  air  withdrawn  from  the  chamber  in  the 
sample,  since  there  were  0.0554  gram  of  water  and  0.0441  gram  of  car- 
bon dioxide  absorbed  in  the  U  tubes  before  the  air  entered  the  meter. 
By  converting  these  weights  to  volume  by  means  of  the  standard  log- 
arithmic factors,  .09462  and  .70680,  we  find  there  was  withdrawn  from 
the  air  system  in  the  sample  0.069  liter  of  water  vapor  and  0.022  liter 
of  carbon  dioxide,  thus  showing  that  the  total  volume  of  air  withdrawn 
in  the  process  of  taking  a  sample,  %,  was  8.672  +  0.069  +  0.022  =  8.763 
liters.  The  logarithm  of  this  amount  is  .94265  and  the  cologarithm 
•O5735-  This  is  more  clearly  expressed  algebraically  as  follows : 

ULATION  Of  TRUE  VOLUME    OP  SAMPLE    FOR  DETERMINATION  OF  CARBON 
DIOXIDE  AND    WATER. 

v0  =  volume  of  air  sample  containing  carbon  dioxide  and  water 

vapor  at  o°  and  760  mm. 

v   =  apparent  volume  of  sample  (i.  e.,  meter  reading). 
/   =  factor  for  correcting  meter  readings. 
w  =  weight  of  water  in  sample. 
wl=  weight  of  carbon  dioxide  in  sample. 

1.2434  w  =  theoretical  volume  of  water  vapor  at  o°  and  760  mm. 
0.5091  zv1  =  volume  of  carbon  dioxide  at  o°  and  760  mm. 
Tm=  temperature  of  water  (air)  in  meter. 
e   =  tension  of  aqueous  vapor  at  Tm  (millimeters  of  mercury). 
m  =  manometer  reading,  expressed  in  millimeters  of  mercury. 


86  A   RESPIRATION   CALORIMETER. 

h  =  height  of  barometer  (in  millimeters),  corrected  to  o°. 
p  =ti  —  e  —  m, 

-  +  L24334  »  +  0.5091  »•. 


CALCULATION  OF  THE  TRUE  VOLUME  OF  AIR  IN  THE  CLOSED  AIR-CIRCUIT. 

The  apparent  volumes  of  air  in  the  different  portions  of  the  air- 
circuit  are,  as  has  been  stated  before,  subject  to  fluctuations,  the  most 
noticeable  of  which  is  the  variation  in  the  quantity  of  air  inclosed  in  the 
pans.  Volume  I,  that  portion  of  the  air  in  the  air-chamber  and  the  air- 
pipe  and  blower  and  the  first  water-  absorber  (see  p.  80),  is  subject  to 
fluctuations  which  may  normally  occur  inside  the  respiration  chamber, 
such  as  interchange  of  'air  through  the  food  aperture,  respiratory  loss, 
etc.,  in  addition  to  the  normal  changes  as  affected  by  temperature  and 
pressure.  The  record  of  the  apparent  volume  of  air  is  given  at  the 
right-hand  side  of  the  residual  sheet  (p.  84)  .  In  this  particular  instance 
the  initial  apparent  volume  of  air  in  section  I  is  4,909.88  liters,  to 
which  a  correction  of  +  0.05  is  added  for  the  respiratory  loss,1  thus 
making  a  total  volume  of  4,909.93  liters.  This  volume  of  gas  is  at  a 
temperature  (T0)  of  20.79°  and  at  a  barometric  pressure  of  755.78  mm. 
To  reduce  this  volume  to  that  under  standard  conditions  of  temperature 
and  pressure  the  logarithm  of  the  volume  is  added  to  the  cologarithm  of 
the  correction  for  temperature  and  the  logarithm  for  pressure,  which  are 
taken  from  tables  prepared  for  convenience.  The  cologarithm  of  the 
correction  for  the  temperature  (T0)  20.79°  is  .96806  and  the  logarithm 
for  reducing  the  barometric  pressure  is  .99758.  On  adding  these  three 
factors  together  it  is  found  that  the  corrected  volume  under  standard 
conditions  is  4,536.40  liters.  This  calculation  is  carried  out  on  the 
left-hand  lower  side  of  the  sheet. 

The  apparent  volume  of  air  in  section  II,  the  air-pipe  leading  from 
the  chamber,  the  blower,  and  entrance  pipe  to  the  first  water-absorber 
is  equal  to  6.55  liters  measured  at  a  temperature  (Tx)  of  20.0°  and 
under  the  same  barometric  pressure  as  I.  To  reduce  this  volume  to 
standard  conditions  a  similar  process  is  carried  out,  the  calculation 
being  placed  immediately  beneath  the  first  on  the  sheet,  and  we  find 
that  the  volume  6.55,  when  reduced  to  standard  conditions,  becomes 
6.07  liters.  Since  both  these  volumes  contain  water  vapor,  they  are 
added  together,  their  sum  giving  V^  the  volume  of  the  air  containing 
water  vapor. 

1  For  calculation  of  respiratory  loss  for  this  particular  period,  see  the  record  sheet 
on  page  64. 


CALCULATION   OF   RESULTS.  87 

The  air  in  section  III  is  subject  to  a  fluctuation  as  a  result  of  the 
increase  in  volume  in  the  first  water-absorber,  and  consequently  the 
initial  volume  in  this  particular  case,  14.60,  must  be  decreased  by  the 
volume  of  the  water  absorbed,  0.04,'  yielding  a  volume  of  14.56  liters. 
This  volume  is  likewise  reduced  to  standard  conditions,  and,  since  it 
contains  carbon  dioxide,  the  reduced  volume,  i.  e.,  13.49,  is  added  to  the 
volume  of  Vu  giving  4,555.96  liters  as  the  volume  of  air  containing 
carbon  dioxide,  i.  e.,  V2. 

The  air  in  section  IV  consists  of  the  constant  volume  of  41. 08  liters, 
which  represents  the  volume  of  the  air-pipes  and  the  fluctuating  vol- 
ume inclosed  in  the  pans.  The  amount  so  inclosed  during  this  particular 
period  is  13.7  liters,2  making  a  sum  total  of  54.78  liters.  The  apparent 
volume  of  air  in  section  IV  is  also  reduced  to  standard  conditions,  and 
when  so  reduced  it  amounts  to  50.75  liters,  which,  when  added  to  V2, 
equals  4,606.71  liters,  or  V3,  the  total  volume  of  air  in  the  system. 

TOTAL  RESIDUAL  WATER  VAPOR. 

Since  the  amount  of  water  vapor  in  the  sample  and  the  corrected 
volumes  of  both  sample  and  residual  air  are  known,  the  calculation  of 
the  total  residual  amount  of  water  vapor  is  a  simple  matter.  The 
computations  are  made  on  the  right  of  the  residual  sheet.  To  the  log- 
arithm of  the  weight  of  water  found  in  the  air  sample  are  added  the 
cologarithm  of  the  corrected  volume  of  air  withdrawn  in  the  sample  v0 
and  the  logarithm  of  the  corrected  volume  Vx  of  residual  air  contain- 
ing water  vapor.  In  the  instance  here  cited  there  were  28.72  grams 
of  water  vapor  in  the  air-circuit. 

It  is  convenient  to  know  not  only  the  weight  of  water  vapor  in  the 
air,  but  also  the  volume,  and  consequently  the  computation  is  carried  a 
step  farther  by  adding  the  logarithmic  factor  .09462  to  the  logarithm 
of  the  weight  of  water,  thus  indicating  that  35.71  liters  of  water  vapor 
were  in  the  system. 

TOTAL  RESIDUAL  CARBON  DIOXIDE. 

The  residual  amount  of  carbon  dioxide  in  the  whole  closed  circuit  is 
determined  in  a  similar  manner,  i.  e.,  by  adding  together  the  logarithm 
of  the  weight  of  carbon  dioxide  found  in  the  sample,  the  cologarithm  of 
the  corrected  volume  of  air  taken  for  a  sample,  vat  and  the  logarithm 
of  the  total  volume  of  air  containing  the  carbon  dioxide  (V2),  i.  e.,  the 

JThe  calculation  for  the  amount  of  air  displaced  by  the  water  absorbed  is  made 
on  the  sheet,  page  64. 
2  For  the  calculation  of  this  volume  of  air,  see  the  record  sheet,  page  64. 


88  A   RESPIRATION    CALORIMETER. 

corrected  volume  of  air  in  the  chamber  and  air-pipes  up  to  the  second 
soda- lime  cylinder.  The  weight  of  carbon  dioxide  in  the  system  at  the 
end  of  the  period  cited  was  22. 93  grams.  By  the  use  of  the  logarithmic 
conversion  factor  .70680  this  weight  of  carbon  dioxide  is  found  to 
correspond  to  11.67  liters. 

OXYGEN  AND  NITROGEN. 

The  residual  volume  of  oxygen  and  nitrogen  together  is  readily  de- 
termined by  deducting  the  volumes  of  water  vapor  and  carbon  dioxide 
from  the  total  corrected  volume  of  air  in  the  system,  V3.  By  reference 
to  page  84  it  will  be  seen  that  the  carbon  dioxide  and  water  occupied 
a  volume  of  47.38  liters.  On  deducting  this  volume  from  V3,  i.  <?., 
4,606.71  liters,  the  volume  of  the  remaining  gas,  oxygen,  and  nitrogen 
is  equal  to  4,559.33  liters.  What  portion  of  this  volume  is  nitrogen 
can  be  found  by  direct  calculation. 

THE  NITROGEN  IN  THE  SYSTEM. 

The  amount  of  nitrogen  present  in  the  system  at  the  beginning  of  an 
experiment  is  determined  directly  by  an  analysis  of  the  air,  from  which 
the  oxygen  is  removed  by  means  of  potassium  pyrogallate.  From  this 
analysis  the  composition  of  the  air  free  from  carbon  dioxide  is  obtained, 
i.  e.,  the  percentages  of  nitrogen  and  oxygen.  From  the  apparent  vol- 
ume, the  true  volume  of  the  gases  in  the  system  is  calculated,  and,  with 
due  allowance  for  the  volume  of  carbon  dioxide  and  water  vapor,  the 
initial  volume  of  nitrogen  present  may  be  computed.  This  volume  is 
commonly  referred  to  as  the  base  line.  Nitrogen  may  enter  the  system 
in  either  one  or  both  of  the  following  ways  :  ( i )  With  the  oxygen  in 
the  steel  cylinders ;  from  2.5  to  8  per  cent  of  the  contents  of  the  cylin- 
der is  nitrogen.  Inasmuch  as  each  cylinder  varies  in  composition  and 
the  amount  of  oxygen  and  nitrogen  must  be  known  for  each  cylinder,  it 
is  necessary  to  make  an  analysis  before  the  cylinder  is  used.  (Seep.  34.) 
(2)  In  air  admitted  through  the  food  aperture. 

Nitrogen  may  leave  the  system  either  in  small  quantities  through 
the  food  aperture  by  the  interchange  of  material,  through  loss  in 
changing  absorbers,  or  in  the  sample  removed  for  the  determinations 
of  oxygen,  but  more  especially,  however,  in  the  large  sample  of  air 
rejected  from  time  to  time. 

In  addition  to  these  regular  channels  for  the  escape  of  nitrogen,  any 
leakage  of  air  out  of  the  system  through  defects  in  the  couplings  or 
connections  obviously  carries  with  it  a  large  amount  of  nitrogen.  The 
discussion  of  this  point  will  be  deferred  until  later. 


CALCULATION   OP   RESULTS.  89 

CALCULATIONS   FOR   NITROGEN. 

It  will  be  noted  that  at  the  top  of  the  sheet  (p.  84),  the  first  space 
below  the  heading  is  arranged  for  the  calculation  of  the  amount  of 
nitrogen.  The  amount  of  nitrogen  in  liters  found,  either  by  analysis 
or  calculation,  in  the  chamber  at  the  beginning  of  the  experimental 
period  is  first  recorded.  In  case  air  has  been  rejected  during  the  period, 
as  explained  on  page  67,  the  number  of  liters  of  air,  the  percentage 
of  nitrogen,  and  the  number  of  liters  of  nitrogen  thus  lost  are  then 
deducted.  The  negative  correction  for  the  amount  of  the  nitrogen 
removed  with  the  absorbers  and  the  positive  correction  for  the  amount 
admitted  with  the  oxygen  are  then  added,  together  with  a  correction 
for  the  interchange  through  the  food  aperture,  if  any,  which  may  be 
either  positive  or  negative,  according  to  whether  nitrogen  was  admitted 
or  removed.  On  applying  these  corrections,  the  nitrogen  present  at 
the  end  of  the  period  is  found.  This  value  may  then  be  transferred 
to  the  next  residual  sheet  under  the  heading  ' '  Volume  of  nitrogen  in 

chamber  at m liters,"  and  serves  as  the  basis  of  new  nitrogen 

calculations  until  a  new  analysis  has  been  completed. 

This  method  of  calculation  assumes  that  there  is  no  free  nitrogen 
eliminated  from  the  body  other  than  that  entering  and  leaving  the 
lungs  in  the  free  state  ;  in  other  words,  that  there  is  no  production  of 
free  nitrogen  from  food  or  body  protein.  That  this  is  probably  the 
case,  all  experimental  evidence  thus  far  seems  to  show,  although  the 
desirability  of  an  absolute  demonstration  is  obvious. 

Furthermore,  it  is  assumed  that  there  is  no  unaccounted-for  leakage 
of  nitrogen  into  or  out  of  the  system.  Indeed,  as  will  be  explained 
beyond,  this  calculation  is  used  ultimately  to  detect  a  leak. 

CALCULATION   FOR  TOTAL  RESIDUAL  OXYGEN. 

From  the  total  volume  of  oxygen  and  nitrogen  determined  by  de- 
ducting the  volumes  of  carbon  dioxide  and  water  from  the  total  air 
volume,  V3,  is  deducted  the  volume  of  the  nitrogen  as  computed  at  the 
head  of  each  residual  sheet.  In  this  instance,  the  volume  of  oxygen 
plus  nitrogen  being  4,559.33,  on  deducting  the  computed  residual 
nitrogen,  3,574.58,  the  volume  of  oxygen  was  computed  to  be  984.75 
liters. 

It  is  thus  seen  that  if  the  corrected  volume  of  air  is  known  as  well 
as  the  volume  of  nitrogen,  carbon  dioxide,  and  water  vapor,  the  differ- 
ence is  obviously  the  volume  of  oxygen.  Since  no  other  gases  are 
present  in  any  considerable  amounts,  this  method  seems  to  suffice  for 


9O  A   RESPIRATION   CALORIMETER. 

all  practical  purposes.  It  is  seen  that  this  method  determines  oxygen 
by  difference,  while  usually  the  factor  in  air  analyses  that  is  determined 
by  difference  is  the  nitrogen. 

The  calculation  may  be  expressed  algebraically  in  the  following  way  : 

z>0  =  volume  of  air  sample. 

Vj  =  volume  of  air  containing  water  =  (I  +  II). 

V2  =  volume  of  air  containing  CO2  =  (I  +  II  +  III)  . 

V3  —  volume  of  air  containing  O  +  N  =  (I  +  II  +  III  +  IV). 

a   =  total  volume  of  water  vapor. 

b   =  total  volume  of  carbon  dioxide. 

c    =  total  volume  of  nitrogen. 

d  —  total  volume  of  oxygen. 

W=  total  weight  of  water  vapor  in  system;  w—  weight  in  air 

sample. 

W'=  total  weight  of  CO2  in  system  ;  wl  =  weight  in  air  sample. 
W  =  «'XV1  Tpi^XV. 

^0  »« 

i.  2434  a>  XV!  ,      .5091  w1  XV, 

- 


It  was  formerly  assumed  that  at  the  beginning  of  the  experiment 
^=.2091  (Vg—  a  —  £);  ^=.7909  (V3—  a  —  £). 

These  values  for  the  amounts  of  oxygen  and  nitrogen  were  deter- 
mined by  assuming  the  composition  of  the  air  free  from  carbon  dioxide 
and  water  vapor  as  20.91  per  cent  oxygen  and  79.09  per  cent  nitrogen. 
We  now  secure  greater  accuracy,  however,  by  using  the  actual  analysis 
of  the  carbon-dioxide  and  water  free  air  as  made  at  the  beginning  of  an 
experiment,  i.  e.,  at  7  a.  m. 

This  consequently  changes  the  factors  used  in  the  last  two  equations 
from  o.  209  1  and  o.  7909  to  those  found  by  analysis.  In  calculating  the 
composition  of  the  air  at  the  end  of  the  first  experimental  period,  c  is 
determined  from  the  record  of  the  amount  of  nitrogen  entering  with 
the  oxygen,  lost  or  gained  through  interchange  through  the  food  aper- 
ture, rejected  with  the  absorbers,  and  lost  if  a  sample  of  air  has  been 
rejected.  All  of  these  corrections  are  applied  to  the  original  initial 
volume  of  nitrogen  found  by  analysis. 

Under  these  conditions,  then,  we  have 

<t=Vs—  (.a+b  +  c). 


CALCULATION   OF   RESULTS.  91 

ACCURACY  OF  CALCULATIONS  OP  THE  RESIDUAL  AMOUNT  OP  OXYGEN. 

In  calculating  the  volume  of  oxygen  remaining  in  the  apparatus  at 
the  end  of  each  experimental  period  according  to  the  method  here  de- 
scribed, it  is  seen  that  the  sum  of  all  the  errors  in  the  determinations 
of  carbon  dioxide  and  water,  as  well  as  the  errors  in  the  calculations  of 
the  different  volumes  in  the  apparatus  and  of  the  nitrogen  admitted, 
affect  directly  the  calculation  of  the  amount  of  oxygen  present.  This 
is  a  serious  defect  in  this  method  of  calculation.  With  the  present 
arrangements  for  sampling  and  analyzing  the  air,  however,  it  is  be- 
lieved that  the  values  obtained  in  a  residual  analysis  represent  very 
correctly  the  actual  amounts  of  water  vapor  and  carbon  dioxide  in  the 
sample.  Similarly  it  is  probably  true  that  the  amount  of  nitrogen  ad- 
mitted to  the  chamber  is  known  with  sufficient  accuracy.  The  main 
source  of  error  therefore  lies  in  the  calculations  of  the  different  vol- 
umes in  the  apparatus,  and  of  the  factors  affecting  these  calculations 
that  of  temperature  is  open  to  the  most  serious  criticism. 

THERMAL  GRADIENT  INSIDE  THE  CHAMBER. 

Inasmuch  as  the  computation  of  the  true  volume  of  the  gas  inside 
the  respiration  chamber  depends  in  large  measure  upon  a  correct 
knowledge  of  the  average  temperature  of  the  mass  of  gas,  it  is  neces- 
sary to  consider  in  detail  the  accuracy  of  its  temperature  measurements. 
While  the  electrical  resistance  thermometers,  both  for  the  air  and  for 
the  copper  wall,  undoubtedly  give  a  very  accurate  measure  of  the  fluctua- 
tions in  temperature  of  their  environment,  it  nevertheless  remains  a  fact 
that  the  inside  of  the  respiration  chamber  contains  a  mass  of  air  which 
is  subjected  in  different  parts  to  widely  varying  temperatures.  In  the 
case  of  the  alcohol  check  experiments  we  have  a  thermal  gradient  extend- 
ing from  the  high  temperature  of  the  alcohol  flame  down  to  the  tempera- 
ture of  the  incoming  water  of  the  heat- absorbing  system.  In  this  case 
great  heat  is  concentrated  at  one  point,  while  the  cooling  area,  i.  <?.,  the 
area  of  the  absorbers,  is  quite  extensive.  In  the  case  of  experiments 
with  man  we  have  a  body  temperature,  which  on  the  surface  is  not  far 
from  33°,  affecting  a  relatively  large  area,  and  a  cooling  area  similar 
to  that  during  the  alcohol  check  experiments.  In  severe  work  experi- 
ments we  have  the  body  more  or  less  exposed  and  the  temperature  of 
the  absorbing  system  cooled  nearly  to  zero.  It  is  therefore  difficult 
to  see  how  the  electrical  resistance  thermometers,  distributed  as  shown 
in  figure  33,  can  in  any  way  assume  accurately  the  average  temperature 
of  the  air  in  the  whole  chamber.  During  rest  experiments  and  alcohol 


92  A   RESPIRATION   CALORIMETER. 

check  experiments  the  discrepancies  are  not  so  great  as  during  work 
experiments  with  men,  but  it  is  clear  that  slight  disturbances  in  either 
the  heat-radiating  surface  or  in  the  heat-absorbing  surface  will  make 
considerable  differences  in  the  average  temperature  of  the  total  volume 
of  air. 

With  alcohol  check  experiments  this  factor  is  practically  a  constant 
one,  and  while  the  electrical  resistance  thermometers  may  not  represent 
the  average  temperature  in  the  system,  at  the  same  time,  owing  to  the 
constancy  of  the  thermal  gradient,  they  probably  record  accurately  any 
differences  in  temperature,  and  it  is  these  alone  which  affect  the  volume 
of  air. 

In  experiments  with  man  the  temperature  factor  could  be  eliminated 
were  it  possible  to  have  the  heat-radiating  surface  constant  throughout 
the  whole  period.  With  variations  in  position,  muscular  activity, 
changes  in  clothing,  bedding,  etc.,  however,  it  is  very  difficult,  if  not 
indeed  absolutely  impossible,  to  measure  the  differences  of  the  average 
temperature  of  the  air  at  the  beginning  and  end  of  each  period.  This 
is  most  noticeable  in  the  case  of  work  experiments,  where  in  the  morn- 
ing at  7  a.  m.  the  subject  is  lying  quietly  in  bed  asleep,  and  at  the  end 
of  the  period,  93.  m.,  he  is  riding  a  bicycle  ergometer  at  a  high  rate 
of  speed.  Again,  at  n  o'clock  at  night  the  subject  is  sitting  dressed, 
possibly  reading  or  writing,  and  at  i  a.  m.  he  is  sound  asleep,  covered 
with  bed-clothing.  It  is  during  these  two  periods,  when  the  widest 
variation  in  bodily  activity  naturally  takes  place,  that  we  find  the 
greatest  discrepancies  in  the  measurement  of  the  volume  of  oxygen. 
These  discrepancies  are  indicated  generally  by  abnormal  values  for  the 
"respiratory  quotient. "  (Seep.  184.)  In  the  particular  experiment  the 
results  of  which  are  presented  in  this  report  (p.  177)  these  discrepancies 
do  not  appear. 

CONCLUSION  REGARDING  THE  ACCURACY  Of  THE  OXYGEN   COMPUTATION. 

This  method  of  calculation  is  found  to  be  far  more  practicable  and 
on  the  whole  more  satisfactory  at  the  present  state  of  our  experimenta- 
tion than  a  method  depending  upon  analyses  of  air  at  the  end  of  each 
period  ;  for  the  difficulties  in  securing  proper  temperature  measure- 
ments of  the  large  volume  of  air  affect  alike  the  calculation  of  the  total 
residual  oxygen  whether  the  analysis  of  a  sample  is  made  by  the  most 
approved  methods  or  whether  the  computation  method  is  employed.  It  is 
therefore  believed  that  the  errors  involved  in  the  system  of  calculations 
as  above  outlined  are  certainly  no  greater  than  those  that  necessarily 
occur  in  using  direct  analyses  of  oxygen  under  present  conditions. 


CALCULATION   OF   RESULTS.  93 

CHECK  ON  THE  COMPUTATION  METHOD  OF  DETERMINING  OXYGEN. 

The  method  of  computation  outlined  on  pp.  86-90  gives  the  amounts 
of  oxygen  and  nitrogen  present  in  the  air  at  the  end  of  each  period  ; 
consequently  at  the  end  of  any  experimental  period  we  can  calculate 
the  percentage  composition  of  air  free  from  carbon  dioxide  and  water 
in  the  system.  If  we  make  such  a  calculation  at  the  end  of  a  24-hour 
period  and  then  make  an  actual  analysis  of  the  air  free  from  carbon 
dioxide  and  water  at  the  end  of  this  period,  we  can  obviously  compare 
the  computed  percentage  of  nitrogen  and  oxygen  in  the  air  with  that 
actually  found  by  analysis.  If  the  sample  for  analysis  is  taken  at  7 
o'clock  in  the  morning,  i.  <?.,  when  the  subject  is  asleep  and  the  tem- 
perature condition  (thermal  gradient)  inside  the  chamber  is  closely 
comparable  to  that  of  the  day  before,  there  is  every  reason  to  believe 
that  the  computed  percentage  composition  and  that  actually  found  will 
be  practically  identical.  Thus,  in  the  actual  experiment  recorded  on 
page  84,  the  percentage  of  oxygen  as  calculated  was  21.60  and  the 
analysis  for  that  period  gave  21.62.  In  fact,  so  uniform  are  these  per- 
centages that  any  difference  in  composition  is  ascribed  to  a  leak  of  air 
into  or  out  of  the  system. 

In  case  an  error  has  been  introduced  in  some  way,  it  may  in  many 
cases  be  accounted  for  by  careful  inspection  of  the  various  divisions  of 
the  calculations.  When  desirable,  a  new  nitrogen  "baseline"  may 
be  determined  by  using  the  results  of  the  chemical  analysis,  after  which 
the  calculations  are  made  as  before.  The  increase  or  decrease  in  the 
amount  of  nitrogen  in  the  new  base  line  is  that  which  has  leaked  into 
or  out  of  the  system. 

COMPUTATION   OF   TOTAL   CARBON-DIOXIDE   AND   WATER   OUTPUT 
AND   OXYGEN   INTAKE. 

Having  considered  in  detail  the  methods  of  calculating  the  residual 
amounts  of  carbon  dioxide,  water,  and  oxygen  in  the  air,  it  is  evident 
that  it  is  possible  to  use  the  data  obtained  by  such  calculations  to  com- 
pute the  total  output  of  carbon  dioxide  and  water  and  intake  of  oxygen 
during  any  given  period. 

TOTAI,  CARBON-DIOXIDE  OUTPUT. 

If  the  total  amount  of  carbon  dioxide  remaining  in  the  chamber  at 
the  end  of  the  period  is  the  same  as  that  at  the  beginning,  obviously 
the  total  output  during  this  period  is  the  weight  of  carbon  dioxide  ab- 
sorbed in  the  carbon- dioxide  absorbing  system.  It  is  very  rare,  how- 


94  A   RESPIRATION   CALORIMETER. 

ever,  that  these  residual  amounts  do  not  vary  between  the  beginning 
and  the  end  of  the  period,  and  consequently  it  is  necessary  to  make 
due  allowance  for  such  fluctuations.  If,  for  example,  at  7  a.  m.  the 
residual  amount  of  carbon  dioxide  is  22.93  grams,  and  at  9  a.  m.,  at 
the  end  of  the  first  two-hour  experimental  period,  the  residual  amount 
of  carbon  dioxide  is  35.46  grams,  then  during  this  period  the  subject 
has  eliminated  not  only  the  amount  of  carbon  dioxide  collected  in  the 
absorbing  system,  but  has  added  to  the  store  in  the  air  in  the  chamber 
12.53  grams,  and  consequently  the  total  output  for  this  period  would 
be  w,  the  weight  absorbed  in  the  absorbing  system,  plus  12.53.  Simi- 
larly, if  the  amount  of  carbon  dioxide  residual  in  the  chamber  at  n 
p.  m.  is  31.26  grams  and  at  i  a.  m.  24.92  grams,  it  is  apparent  that 
the  carbon  dioxide  absorbed  in  the  absorbing  system  represents  not 
only  that  given  off  by  the  subject  during  this  period,  but  also  the 
difference  between  the  residual  amount  at  n  p.  m.  and  that  at  i  a.  m., 
namely,  6.34  grams,  and  consequently  the  total  output  of  the  subject 
during  this  period  is  w,  the  weight  absorbed  in  the  absorbing  system, 
minus  6.34,  the  amount  removed  in  the  residual  air.  This  calculation 
is  carried  out  for  convenience  in  a  table  in  which  the  residual  amounts, 
as  well  as  those  weighed  in  the  absorbers,  are  recorded  and  the  proper 
corrections  applied.  (See  p.  183.) 

TOTAL  OUTPUT  OF  WATER  VAPOR. 

The  fluctuations  in  the  residual  amounts  of  water  vapor  affect  the 
total  weight  of  water  absorbed  in  the  water- absorber  in  a  manner  pre- 
cisely similar  to  that  in  which  the  residual  amounts  of  carbon  dioxide 
affect  the  weights  of  carbon  dioxide.  If  during  an  experimental 
period  there  has  been  an  increase  in  the  amount  of  water  vapor  in  the 
air,  then  the  total  output  of  water  vapor  during  this  period  must  be 
the  weight  of  water  collected  in  the  absorbing  system  plus  the  increase 
in  the  residual  amount,  and  conversely,  if  there  has  been  a  diminution 
in  the  residual  amount,  this  diminution  must  be  subtracted  from  the 
weight  of  water  in  the  absorbers  to  give  the  true  output  for  the  period. 
In  all  discussions  thus  far  with  regard  to  water,  the  assumption  has 
been  made  that  the  water  exists  in  the  form  of  water  vapor.  Since, 
however,  certain  parts  of  the  interior  of  the  respiration  chamber  are 
frequently  at  a  temperature  below  the  dew-point  of  the  air  inside  the 
chamber,  there  may  be  a  very  material  condensation  of  water  on  these 
colder  parts.  When  the  heat-absorbing  system,  through  which  the  cold 
water  to  bring  away  the  heat  passes,  is  actually  below  the  dew-point, 
it  becomes  covered  with  moisture,  and  in  certain  classes  of  experi- 


CALCULATION   OF  RESULTS.  95 

ments,  namely,  where  excessive  muscular  exercise  is  performed,  the 
condensation  of  moisture  may  be  so  great  as  to  cause  the  condensed 
moisture  to  drop  off  and  collect  in  troughs  which  are  specially  provided 
for  this  purpose.  The  water  thus  collected  may  in  some  experi- 
ments amount  to  several  liters,  and  this  amount  must  be  duly  consid- 
ered when  calculating  the  total  output  of  water  from  the  body.  This 
condensed  water  is  commonly  termed  the  ' '  drip ' '  water,  and  its  col- 
lection is  described  in  detail  on  page  23  in  connection  with  the  water- 
absorbing  apparatus.  In  the  final  calculations,  therefore,  for  the  total 
water  output,  we  take  into  consideration  not  only  the  fluctuations 
in  the  residual  amounts  of  water  vapor  in  the  air  of  the  chamber,  but 
also  the  amount  of  condensed  water  on  the  absorbing  system.  The 
amount  of  water  thus  condensed  is  readily  determined  by  weighing  the 
heat-absorbing  system.  (See  p.  161 . )  In  all  alcohol  experiments  and  in 
rest  experiments  with  men,  care  is  taken  to  regulate  the  temperature 
of  the  water  which  brings  away  the  heat,  so  that  the  heat-absorbing 
system  is  never  cooled  below  the  dew-point.  Condensation  of  moisture 
and  the  necessity  for  collecting  drip  water  are  thereby  obviated,  and 
it  is  therefore  seldom  necessary  to  make  this  correction  except  in  work 
experiments. 

The  tabular  form  for  computing  the  total  output  of  water  is  given  on 
page  181. 

COMPUTATION  FOR  TOTAL  INTAKE  OF  OXYGEN. 

Fluctuations  in  the  residual  amounts  of  oxygen  are  usually  much 
greater  than  the  fluctuations  in  the  residual  amounts  of  water  vapor, 
and  consequently  it  is  more  often  important  to  take  these  fluctuations 
into  consideration.  The  variations  in  the  residual  amounts  of  oxygen 
are  expressed  in  terms  of  liters.  By  dividing  by  the  factor  0.7,  the 
amount  in  liters  is  converted  to  the  weight  in  grams.  The  corrections 
for  the  variations  in  the  residual  amount  are  applied  to  the  weight  of 
oxygen  admitted  from  the  steel  cylinders.  If  the  amount  of  oxygen 
remaining  in  the  chamber  at  the  end  of  the  given  period  is  less  than  at 
the  beginning,  the  weight  of  the  amount  of  oxygen  thus  used  must  be 
added  to  the  weight  admitted  with  the  cylinders  to  obtain  the  true 
weight  of  oxygen  consumed  by  the  subject.  Conversely,  when  there 
has  been  a  storage  of  oxygen  in  the  system  in  a  given  period,  the 
amount  thus  stored  must  be  deducted  from  that  admitted  from  the  steel 
cylinders.  The  tabular  form  for  computations  is  shown  on  page  184. 


96  A    RKSPIRATION   CALORIMETER. 


ALCOHOL  CHECK  EXPERIMENTS. 

While  from  a  consideration  of  the  construction  of  the  apparatus  it  is 
difficult  to  conceive  of  any  loss  or  gain  of  carbon  dioxide,  water,  or 
oxygen  to  the  system  other  than  that  occurring  through  regular  chan- 
nels and  accounted  for  by  the  regular  analyses,  it  still  remains  necessary 
to  demonstrate  the  practicability  and  accuracy  of  the  apparatus  for 
determining  the  quantity  of  these  substances  entering  into  an  actual 
experiment.  If  a  known  amount  of  carbon  dioxide  could  be  liberated 
inside  the  chamber  and  then  reabsorbed  by  the  purifying  system  and 
the  difference  in  the  composition  of  the  residual  air  taken  into  consid- 
eration, the  amounts  thus  recovered  should  agree  exactly  with  that 
introduced.  In  earlier  experimenting  attempts  were  made  to  do  this. 
Similarly,  a  certain  amount  of  water  was  vaporized  in  the  chamber  and 
recovered  again  in  the  ventilating  current  of  air.  The  difficulty  of  a 
proper  absorbent  for  oxygen  whereby  oxygen  could  be  absorbed  on  a 
large  scale  precludes,  however,  testing  the  apparatus  by  measuring  with 
this  or  any  similar  process  the  amount  of  oxygen  utilized. 

It  is  possible,  however,  by  burning  a  known  weight  of  a  substance 
inside  the  chamber  not  only  to  produce  a  known  weight  of  carbon 
dioxide  and  water,  but  also  to  use  in  oxidation  a  known  weight  of 
oxygen.  As  a  result  of  our  previous  experience  in  testing  the  earlier 
forms  of  this  apparatus,  we  now  burn  known  weights  of  ethyl  hydroxide 
inside  the  chamber  and  determine  the  amounts  of  carbon  dioxide  and 
water  eliminated  and  oxygen  absorbed.  Considerable  preliminary  ex- 
perimenting l  has  shown  that  when  ethyl  hydroxide  is  burned  in  a 
so-called  Argand  burner  no  products  of  oxidation  other  than  carbon 
dioxide  and  water  vapor  are  present  in  any  material  amounts.  Con- 
sequently it  becomes  necessary  simply  to  introduce  into  the  chamber  a 
given  weight  of  alcohol  and  burn  it,  absorbing  the  carbon  dioxide  and 
water  vapor  and  measuring  the  amount  of  oxygen  required  for  oxidation. 

KIND  OF  ALCOHOL  USED. 

For  testing  an  apparatus  of  this  kind  the  use  of  ethyl  alcohol  has 
proved  extremely  satisfactory.  The  chief  objection  attending  its  use  is 
the  fact  that  its  absolute  composition  is  not  easily  determined,  since  the 
elementary  organic  analysis  of  alcohol  is  attended  with  considerable  diffi- 
culty. It  is  not  easy  to  weigh  accurately  and  transfer  completely  to  a 
combustion  tube  any  liquid,  and,  in  addition,  alcohol  is  especially  prone 
to  take  on  water,  and  hence  the  use  of  absolute  alcohol  is  practically 

'U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63,  p.  60. 


ALCOHOL   CHECK   EXPERIMENTS.  97 

prohibited.  Nevertheless,  it  is  possible  by  means  of  determinations  of 
specific  gravity  and  by  reference  to  standard  tables  to  determine  with 
great  accuracy  the  percentage  of  absolute  ethyl  hydroxide  present  in  a 
mixture  of  alcohol  and  water.  This  procedure  assumes,  however,  at 
the  outset  that  the  liquid  under  examination  contains  only  these  sub- 
stances. With  many  of  the  modern  methods  of  preparing  alcohol  the 
final  product  is  frequently  contaminated  with  alcohols  of  a  higher  car- 
bon content.  The  ultimate  result  of  the  presence  of  these  alcohols  is 
twofold.  In  the  first  place,  it  alters  the  specific  gravity  of  the  mixture  ; 
in  the  second  place,  inasmuch  as  the  percentage  of  oxygen  is  lower, 
the  amount  of  carbon  and  hydrogen  in  each  gram  of  substance  is  greater 
with  the  higher  alcohols  than  with  ethyl  alcohol.  That  these  impuri- 
ties are  present  in  minute  quantities  in  the  different  grades  of  commer- 
cial alcohol  is  doubtless  true,  but  with  the  grades  of  alcohol  that  we 
have  so  far  experimented  with — those  ordinarily  purchased  from  distillers 
for  use  in  biological  and  chemical  laboratories — we  have  had  as  yet  no 
evidence  of  the  existence  of  higher  alcohols  in  quantities  sufficient  to 
influence  our  results.  We  therefore  rely  upon  the  determination  of 
specific  gravity  for  a  calculation  of  the  amounts  of  carbon  dioxide  and 
water  that  should  be  yielded  by  one  gram  of  the  alcohol. 

DETERMINATION  OF  SPECIFIC  GRAVITY. 

By  means  of  the  pyknometer,  devised  and  described  by  Squibb,1  it  is 
possible  to  determine  the  specific  gravity  of  a  mixture  of  alcohol  and 
water  to  the  fifth  or  even  sixth  decimal  place. 

This  pyknometer  is  so  constructed  that  when  immersed  in  water  at 
a  temperature  of  15.6°,  50  grams  of  recently  boiled,  distilled  water  fills 
the  bottle  and  the  graduated  stem  to  an  arbitrary  number  on  the  scale. 
With  the  pyknometer  now  in  use  the  stem  is  graduated  from  o  to  70, 
and  we  have  found  that  when  the  level  of  water  (bottom  of  the  menis- 
cus) stands  at  42.5,  the  bottle  contains  50  grams  of  distilled  water.  By 
removing  water  with  a  small  strip  of  bibulous  paper  it  was  found  that 
each  division  on  the  scale  corresponds  to  a  change  in  the  weight  of 
water  amounting  to  1.8  mg. 

The  pyknometer  is  first  carefully  dried,  a  very  thin  film  of  vaseline 
applied  to  the  ground  glass  stopper  in  the  neck,  and  the  apparatus 
accurately  weighed.  The  bottle  is  then  filled  with  alcohol  which  has 
previously  been  cooled  in  a  well-stoppered  bottle  or  flask  to  10°  or  12°, 
the  graduated  top  inserted,  and  the  bulb  immersed  in  water  at  from 
15°  to  1 6°.  A  lead  collar  fitting  over  the  neck  of  the  bottle  holds  it 

'Journ.  Am.  Chem.  Soc.  (1897),  19,  p.  in. 
7B 


98  A   RESPIRATION   CALORIMETER. 

in  position  in  the  water  bath.  The  water  is  constantly  stirred  and  the 
temperature  frequently  noted,  with  due  allowances  for  the  calibra- 
tion correction  of  the  thermometer.  When  the  temperature  of  the 
whole  mass  has  reached  15.6°,  the  level  of  the  alcohol  in  the  stem  is 
brought  to  the  graduation  at  42.5.  The  removal  of  alcohol  is  readily 
made  by  means  of  a  finely  drawn-out  glass  tube  and  small  strips  of 
bibulous  paper,  and  all  alcohol  adhering  to  the  upper  part  of  the  stem 
is  carefully  absorbed  by  these  means.  After  the  proper  adjustment  of 
the  level  of  the  liquid,  the  pyknometer  is  removed,  carefully  dried,  and 
weighed.  The  increase  in  weight  is  the  absolute  weight  of  50  cc.  of 
the  alcohol,  and  this  number,  divided  by  50,  gives  the  specific  gravity 
of  the  solution  direct.  The  expansion  of  the  alcohol  after  removal 
from  the  water  bath  causes  the  enlargement  of  the  stem  to  become 
partly  filled  with  alcohol,  but  obviously  this  in  no  wise  affects  the 
weight. 

ALCOHOLOMETRIC  TABLES. 

From  the  specific  gravity  the  percentage  of  alcohol  may  be  obtained 
from  standard  alcohol ometric  tables.  Dr.  E.  R.  Squibb  in  a  personal 
letter  recommended  as  especially  accurate  a  table  published  in  his 
Ephemeris.1  A  more  recent  alcoholometric  table  prepared  by  Morley  * 
is  also  excellent. 

FACTORS  FOR  ACTUAL  AMOUNTS  OF  CARBON  DIOXIDE,  WATER,  AND  OXYGEN. 

The  combustion  of  pure  ethyl  hydroxide  may  be  expressed  by  the 
following  equation  : 

C2H60  +  302  =  2C07  -f-  3H20. 

From  the  molecular  weights 3  of  ethyl  hydroxide,  carbon  dioxide,  and 
water  and  the  atomic  weight  of  oxygen  it  can  be  readily  calculated  that 
one  gram  of  ethyl  hydroxide  when  completely  burned  yields  1.911 
grams  of  carbon  dioxide  and  i .  1 74  grams  of  water,  requiring  for  its 
combustion  2.085  grams  of  oxygen. 

Since  pure  ethyl  hydroxide  is  never  used,  however,  but  rather 
alcohol  diluted  with  about  10  per  cent  of  water,  it  is  necessary  to 
take  into  consideration  the  percentage  of  alcohol  used.  In  general 
the  alcohol  is  not  far  from  91  per  cent  ethyl  hydroxide  by  weight, 
and  in  the  alcohol  check  experiment  given  on  page  102  the  alcohol 
used  consisted  of  90.77  per  cent  of  ethyl  hydroxide. 

1  Ephemeris,  1884-85,  part  2,  pp.  562-577. 
'Journ.  Am   Chem.  Soc.  (1904),  26,  p.  1185. 
8  Atomic  weights  used  are  given  on  page  82. 


ALCOHOI,  CHECK   EXPERIMENTS.  99 

One  gram  of  a  mixture  of  ethyl  hydroxide  and  water  containing 
90.77  per  cent  of  absolute  alcohol  will  give  1.735  grams  of  carbon 
dioxide  and  1.066  grams  of  water,  resulting  from  the  combustion  of 
the  alcohol  molecule,  in  addition  to  the  0.092  gram  of  preformed 
water  present  in  each  gram  of  the  mixture,  and  thus  the  total  amount 
of  water  resulting  from  the  combustion  and  vaporization  of  one  gram 
of  90.77  per  cent  alcohol  is  1.066  -(-0.092  =  1.158  grams. 

If  one  gram  of  the  90.77  percent  alcohol  yields  1.735  grams  of  carbon 
dioxide  and  1.066  grams  of  water,  the  amount  of  oxygen  involved  in 
the  reaction  is  readily  determined  by  adding  the  weights  of  the  carbon 
dioxide  and  water  and  subtracting  the  original  weight  of  the  alcohol  used. 

To  simplify  calculations,  three  logarithmic  factors  are  computed, 
which,  when  added  to  the  logarithm  of  the  weight  of  alcohol  burned, 
yield  the  logarithm  of  the  total  theoretical  amounts  of  carbon  dioxide, 
water,  and  oxygen  involved  in  the  combustion.  These  factors  obvi- 
ously vary  with  the  percentage  of  alcohol  used,  and  consequently  the 
specific  gravity  of  a  rather  large  amount  (5  to  6  liters)  is  taken  and 
the  alcohol  carefully  preserved  in  a  well-stoppered  bottle  for  use  ex- 
clusively in  alcohol  check  experiments. 

AI.COHOI,  LAMP. 

In  earlier  experiments,  when  oxygen  was  not  determined,  it  was  pos- 
sible to  introduce  through  the  food  aperture  a  small  alcohol  lamp  and 
change  it  at  the  end  of  a  period  for  another  one  without  material  alter- 
ation of  the  water  and  carbon-dioxide  content  of  the  air  inside  the 
chamber  ;  but  the  problem  became  complicated  when  the  determination 
of  oxygen  was  undertaken,  and  this  simple  method  was  no  longer 
sufficient.  Consequently  a  special  form  of  lamp  was  devised  by  means 
of  which  the  alcohol  could  be  put  into  the  chamber  without  disturbing 
the  food  aperture  or  the  volume  of  air  inside  the  chamber.  The  lamp 
is  pictured  in  figure  22. 

The  reservoir  of  the  lamp  is  a  bottle  with  an  opening  on  one  side 
near  the  bottom  and  another  in  the  center  of  the  bottom.  The  burner 
is  of  the  ordinary  round  wick,  kerosene,  Argand  type,  and  is  attached  to 
the  neck  of  the  bottle  by  means  of  a  short  length  of  large  rubber  tubing. 
The  wick  is  purposely  long  enough  to  reach  nearly  to  the  bottom  of 
the  bottle.  The  reservoir  is  filled  with  alcohol  through  a  rubber  tube 
extending  from  the  hole  in  the  side  of  the  bottle  through  a  small 
orifice  in  the  outer  door  of  the  food  aperture  to  the  supply  on  the  out- 
side. A  glass  tube  of  small  diameter,  bent  like  a  U  tube,  with  a  long 
and  a  short  arm,  and  with  the  latter  inserted  in  the  opening  in  the 
bottom  of  the  bottle,  serves  to  indicate  the  level  of  the  alcohol  in  the 


IOO 


A    RESPIRATION   CALORIMETER. 


bottle.  For  gross  adjustments,  it  is  possible  to  see  the  level  of  the 
alcohol  through  the  glass  of  the  bottle  ;  but  as  the  alcohol  ascends  in 
the  constricted  portion  of  the  bottle,  and  especially  in  the  rubber  tube 
below  the  metal  burner,  it  is  impossible  to  note  the  exact  level  through 
the  neck  of  the  bottle  itself,  and  consequently  the  side-gage  tube  is 
necessary.  A  bit  of  paper  is  attached  to  this  small  tube  to  indicate  the 
proper  height  to  which  the  bottle  should  be  filled.  The  gage  tube  is 
drawn  out  to  a  fine  jet  at  the  top  to  minimize  evaporation  of  alcohol. 

At  the  beginning  of  an  experiment  the  lamp  is  filled  and  lighted, 
the  chimney  put  in  place,  the  flame  watched  for  several  minutes  to  see 
that  it  is  burning  to  the  proper  height,  and  then  the  chamber  sealed  and 


FIG.  22. — The  Alcohol  Lamp  and  Connections.  The  alcohol  lamp  is  placed  inside  the  respiration 
chamber  and  fed  with  alcohol  through  a  rubber  tube  from  the  burette  on  the  outside.  An 
electric  light  in  front  illuminates  the  gage  on  the  side  of  the  alcohol  lamp,  thus  enabling  it  to 
be  filled  to  the  same  level  each  time. 

the  preliminary  adjustments  of  temperature  made.  The  lamp  burns 
quietly  and  approximately  at  a  constant  rate.  Just  before  the  experi- 
ment begins,  alcohol  is  admitted  through  the  small  rubber  tube  into 
the  glass  bottle  until  the  level  in  the  gage  tube  reaches  the  mark  on 
the  side.  At  this  instant  the  experiment  proper  begins.  At  the  end 
of  the  experimental  period,  which  may  be  two  or  more  hours  in  length, 
the  alcohol  is  again  filled  to  this  level,  and  the  exact  amount  of  alcohol 
required  to  bring  the  meniscus  on  the  gage  tube  back  to  its  former  posi- 
tion, plus  the  amounts  added  to  the  lamp  from  time  to  time,  represents 
the  exact  amount  of  alcohol  burned  during  a  period. 

For  determining  this  amount,  we  use  the  following  method  :    A 
supply  of  alcohol  much  larger  than  would  be  normally  required  during 


CHBT:K  EXPERIMENTS.  101 

an  experiment  is  placed  in  a  glass  bottle  fitted  with  a  two-hole  rubber 
stopper.  Bent  glass  tubes  passing  through  the  holes  in  the  stopper 
provide  the  means  for  forcing  out  the  alcohol  by  blowing  air  into  the 
bottle,  as  in  an  ordinary  laboratory  wash-bottle.  The  tube  through 
which  the  air  enters  the  bottle  is  connected  with  a  chloride  of  calcium 
tube  to  remove  moisture  from  the  air  blown  into  the  bottle.  The  exit 
tube  from  the  alcohol  bottle  is  bent  downward  and  drawn  out  to  a 
point  and  so  placed  that  it  delivers  the  alcohol  into  a  burette  attached 
to  the  outside  of  the  rear  wall  of  the  chamber.  The  burette  is  con- 
nected at  the  bottom  by  means  of  rubber  tubing,  and  a  glass  tube 
through  a  cork  in  the  outer  door  of  the  food  aperture,  with  the  long 
rubber  tube  leading  to  the  alcohol  lamp.  A  screw  pinchcock  controls 
the  flow  of  alcohol  out  of  the  burette. 

At  the  beginning  of  an  experiment  the  observer,  by  looking  through 
the  glass  door  of  the  food  aperture,  notes  the  level  of  alcohol  in  the 
reservoir  of  the  lamp,  and  at  the  exact  moment  when  it  reaches  the 
mark  on  the  gage  tube  he  closes  the  pinchcock  at  the  bottom  of  the 
burette.  The  alcohol  supply  bottle,  with  rubber  stopper  and  glass 
tubes,  is  then  weighed,  and  the  height  of  alcohol  in  the  burette  accu- 
rately noted.  At  the  end  of  the  experiment  the  same  operation  is  re- 
peated, the  lamp  reservoir  being  again  filled  to  the  mark  on  the  gage 
and  the  level  of  the  alcohol  in  the  burette  again  recorded.  The  alco- 
hol supply  bottle  is  then  weighed,  and  the  difference  in  the  weights 
at  the  beginning  and  end,  corrected  for  difference  in  the  amounts  of 
alcohol  in  the  burette,  gives  the  quantity  of  alcohol  burned.  The 
weighing  of  the  bottle  may  be  made  with  sufficient  exactness  on  the 
balance  for  weighing  food,  or  that  for  weighing  the  water  and  carbon- 
dioxide  absorbers. 

During  the  course  of  the  experiment,  as  the  level  of  alcohol  in  the 
alcohol  lamp  becomes  low,  sufficient  alcohol  may  be  admitted  from 
time  to  time  to  keep  the  level  well  above  the  lower  end  of  the  wick. 
This  successive  addition  of  alcohol  needs  no  special  measurement,  since 
it  is  the  total  amount  (loss  in  weight  of  the  bottle)  admitted  during  a 
period  that  is  actually  required.  Furthermore,  there  may  be  differ- 
ences more  or  less  great  in  the  level  of  alcohol  in  the  burette.  It  is 
possible  with  care  to  adjust  this  amount  to  very  nearly  the  same  at  the 
end  of  each  period  by  blowing  over  more  or  less  alcohol  from  the  bottle, 
and  this  is  regularly  done,  though  differences  in  level  of  the  burette  are 
invariably  recorded  and  the  residual  amount  of  alcohol  in  the  burette 
allowed  for  in  the  calculations. 

On  the  particular  burette  used  in  connection  with  this  lamp,  the 
graduations  happened  to  correspond  very  closely  indeed  to  the  weight  of 


102  A   RESPIRATION   CALORIMETER. 

the  volume  of  alcohol  delivered.  This  is  due  to  the  fact  that  this  bu- 
rette is  one  of  the  Geissler  type,  in  which  a  ground  glass  rod  serves  as 
a  stopcock.  Obviously,  therefore,  when  this  glass  rod  is  removed  the 
actual  amount  of  liquid  delivered  between  the  marks  on  the  burette  is 
larger  than  when  the  rod  is  in  place.  This  difference  happens  to  com- 
pensate almost  exactly  for  the  lower  specific  gravity  of  the  alcohol 
used,  and  consequently  the  number  of  cubic  centimeters  read  on  this 
burette  corresponds  to  the  same  number  of  grams  of  alcohol. 

Thus  the  calculation  of  the  amount  of  alcohol  admitted  to  the  lamp 
is  based  upon  the  loss  in  weight  of  the  alcohol  bottle  and  tubes  and 
the  variations  of  alcohol  level  in  the  burette.  The  lamp  here  described 
burns  alcohol  at  the  rate  of  about  20  grams  per  hour. 

The  electric  light  placed  just  outside  the  window  is  so  situated  that 
the  rays  of  light  fall  upon  a  mirror  which  is  inclined  in  such  a  position 
as  to  illuminate  brilliantly  the  gage  tube,  thus  materially  aiding  in  the 
proper  adjustment  of  the  alcohol  level  at  the  end  of  the  period. 

FREQUENCY  AND  DURATION  OF  EXPERIMENTS. 

In  the  earlier  years  of  experimenting  it  was  deemed  advisable  to  con- 
duct an  alcohol  check  test  immediately  before  each  experiment  with 
man.  With  increasing  skill  in  manipulation  the  necessity  for  these 
frequent  tests  has  in  a  large  measure  disappeared,  and  at  present  three 
or  four  tests  in  a  year  are  all  that  are  required  to  control  the  apparatus. 

The  experiments  last  from  8  to  36  or  more  hours.  Recently  experi- 
ments of  about  24  hours  have  been  most  common.  The  experiment 
here  reported  was  subdivided  into  three  periods  of  3  hours  54  minutes, 
5  hours  44  ^  minutes,  and  1 1  hours  52  minutes,  respectively,  the  whole 
experiment  lasting  2 1  hours  30^  minutes.  The  total  amount  of  alcohol 
burned  was  406.8  grams,  apportioned  among  the  periods  as  follows  : 
First  period,  73.4  grams;  second,  108.1  grams,  and  third,  225. 3 grams. 

CALCULATION   OP    THE   ALCOHOL   CHECK   EXPERIMENTS. 

From  the  weight  of  the  alcohol  burned  and  the  known  factors  cor- 
responding to  the  theoretical  amounts  of  carbon  dioxide,  water,  and 
oxygen  per  gram  of  alcohol,  the  theoretical  quantities  that  should  be 
found  by  means  of  the  respiration  apparatus  may  be  readily  computed. 
Inasmuch  as  the  quantities  of  carbon  dioxide,  water,  and  oxygen,  as 
found  by  gain  in  weight  of  the  absorbing  system  and  loss  in  weight  of 
the  oxygen  cylinder  must  be  corrected  for  the  variations  in  the  residual 
amounts  of  these  gases  present  in  the  system  at  the  end  of  each  period, 
it  is  customary  in  tabulating  the  results  of  these  determinations  to  in- 
clude in  the  tables  the  data  for  the  residual  amounts. 


ALCOHOL   CHETK   EXPERIMENTS. 


103 


DETERMINATION  OF  CARBON  DIOXIDE. 

The  computations  for  the  amounts  of  carbon  dioxide  are  given  in 
Table  i. 

TABLE  i. — Record  of  Carbon  Dioxide  in  Ventilating  Air  Current. 
Alcohol  check  experiment,  April  6-7,  1905. 


Date. 

Period. 

Carbon  dioxide. 

(/) 
Ratio 
of 
amount 
found 
to 
amount 
required. 
d-s-e. 

W 

Amount 
in 
chamber 
at  end 
of  period. 

C*) 

Gain  (+) 
or 
loss  (—  ) 
over 
preceding 
period. 

W 

Amount 
absorbed 
from 
air 
current. 

(0 

Total 
found  by 
combus- 
tion. 
c+d. 

w 

Required 
by 
theory. 

April  6  

Preliminary.  .  . 
First  

Grams. 
29.70 

41-35 
32.62 
30.91 

Grams. 
+  11.65 

-8.73 
—  1.71 

Grams. 

115.05 
196.  \2 

393-81 

Grams. 

126.70 

187.39 
392.10 

706.19 

Grams. 

127.32 

187.51 
39081 

705.64 

Per  cent. 

99-5 
99-9 
100.3 

IOO.I 

Do.. 

Do.  . 
April  7  

Second.  . 

Third   

Total 

In  the  first  column  the  date  on  which  the  experiment  was  made  is 
given,  and  in  the  second  column  the  period,  each  experiment  being 
subdivided  into  periods  varying  from  2  to  12  hours  in  duration.  The 
amount  of  carbon  dioxide  in  the  chamber  at  the  beginning  of  the  ex- 
periment is  recorded  in  column  a.  The  subsequent  amounts  of  carbon 
dioxide  found  at  the  end  of  the  periods  are  recorded  beneath  this,  and 
corresponding  corrections  for  fluctuations  in  the  residual  amounts  are 
recorded  in  the  next  column.  If,  then,  these  corrections  are  added  or 
subtracted,  as  the  case  may  be,  to  the  weights  of  carbon  dioxide  ab- 
sorbed in  the  absorbing  system  and  recorded  in  column  c,  the  corrected 
amount  of  carbon  dioxide  produced  by  the  combustion  of  the  alcohol 
is  found.  This  is  recorded  in  column  d.  From  the  computations  of 
the  theoretical  quantities  that  should  be  yielded  from  this  amount  of 
alcohol,  the  data  in  column  e  are  obtained,  and  the  ratio  between  the 
amount  found  and  the  amount  required  by  theory  is  expressed  in  per 
cent  in  the  last  column. 

Obviously,  when  rather  small  amounts  of  alcohol  are  burned  and 
consequently  small  amounts  of  carbon  dioxide  are  evolved  per  period, 
slight  errors  in  the  determination  of  the  residual  amounts  may  result 
in  a  considerable  percentage  error  for  the  short  periods.  The  errors 
are  compensating,  however,  for  if  the  residual  amount  of  carbon  dioxide 
found  in  the  chamber  at  the  end  of  a  given  period  is  lower  than  it  should 
be,  the  error  will  affect  the  total  amount  produced  in  the  preceding 
period  in  one  direction  and  that  produced  during  the  subsequent  period 


104 


A    RESPIRATION   CALORIMETER. 


in  another  ;  consequently  it  is  to  be  expected  that  the  average  of  two  or 
three  periods  would  be  much  more  accurate  than  any  single  period. 
On  the  other  hand,  if  periods  of  10  or  12  hours  in  length  are  consid- 
ered, the  possible  error  in  determination  of  residual  amounts  becomes 
quite  insignificant.  It  would  seem  from  the  experiment  here  reported 
that  the  determination  of  carbon  dioxide  by  this  apparatus,  even  in 
short  periods,  is  extremely  satisfactory. 

DETERMINATION  OF  WATER. 

The  computations  for  the  determination  of  water  in  the  alcohol  check 
experiments  are  made  in  a  manner  quite  similar  to  those  for  carbon  diox- 
ide, the  details  for  this  particular  experiment  being  given  in  Table  2. 

The  column  headings  are  self-explanatory,  and  it  is  seen  that  the 
percentage  error  in  the  determination  of  water  is,  relatively  speaking, 
small.  When  it  is  considered  that  one  of  the  most  difficult  determina- 
tions in  elementary  organic  analysis  or  with  large  respiration  apparatus 
has  been  the  accurate  determination  of  water,  it  is  seen  that  the  accu- 
racy here  obtained  is  much  greater  than  would  be  ordinarily  expected. 
Indeed,  the  accuracy  of  the  water  determination  would  justify  the  use  of 
the  ' '  closed  circuit ' '  were  the  determination  of  oxygen  (its  chief  object) 
not  practicable. 

TABLE  2. — Record  of  Water  in  Ventilating  Air  Current. 

Alcohol  check  experiment,  April  6-7,  1905. 


Date. 

Period. 

(") 
Total 
amount 
of  vapor 
in  cham- 
ber at 
end   of 
period. 

(*) 
Gain  (+) 
or 
loss  (—  ) 
over 
preced- 
ing 
period. 

ft 

Amount 
absorbed 
from 
air 
current. 

(d) 

Total 
found  by 
combus- 
tion. 
c+i>. 

M 

Required 
by 
theory. 

(/) 
Ratio 
of 
amount 
found 
to 
amount 
required. 
d-=re. 

April  6  
Do.  . 

Preliminary.  .  . 
First  

Grams. 
22.72 
20.  4S 

Grams. 
—  2.27 

Grams. 
88.78 

Grams. 
8651 

Grams. 
84.08 

Per  cent. 
IOI.8 

Do  

Second  

21.  IO 

-j-  0.65 

123.68 

124.  •*•* 

125.15 

QQ.'t 

April  7.. 

Third  

20.  1  7 

—  o.()i, 

264.08 

26^.15 

260.83 

IOO.Q 

Total 

47VQQ 

47O.Q6 

100.6 

THE  COMPUTATIONS  FOR  OXYGEN. 

Inasmuch  as  carbon  dioxide  and  water  have  been  determined  by  other 
methods  with  apparatus  as  large  as  this  with  great  accuracy,1  especial 
interest  in  this  particular  form  of  apparatus  lies  in  its  power  for  deter- 


1U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  136,  pp.  37,  38. 


ALCOHOI,  CIT:CK  EXPERIMENTS. 


105 


mining  accurately  the  amount  of  oxygen  consumed,  either  by  men  or 
by  an  alcohol  lamp.  In  Table  3  beyond  are  recorded,  first  the  date 
of  the  experiment,  then  in  succession  the  number  of  the  period,  the 
amount  of  oxygen  residual  in  the  chamber  expressed  in  liters,  and 
the  differences  in  the  amounts  of  oxygen  residual  in  the  chamber  at  the 
beginning  and  end  of  the  different  periods,  expressed  first  in  liters  and 
then  in  grams.  The  weight  of  oxygen  admitted  from  the  steel  cylin- 
der is  next  recorded,  followed  by  the  corrected  amount  of  oxygen  used 
in  the  combustion,  the  theoretical  amount  of  oxygen  required  to  burn 
the  weighed  amount  of  alcohol,  and,  finally,  the  ratio  of  the  amount 
found  to  the  amount  required,  expressed  in  per  cent. 

The  same  considerations  which  affect  the  accuracy  of  computations 
of  this  nature  for  short  periods,  i.  e.,  the  possible  effect  of  errors  in 
residual  analyses,  which  were  discussed  when  considering  the  compu- 
tation of  carbon  dioxide,  also  influence,  perhaps  in  a  more  marked 
degree,  the  computation  of  the  amount  of  oxygen  ;  but  here,  as  in  the 
previous  case,  the  errors  are  more  or  less  compensating,  and,  generally 
speaking,  the  longer  the  period  the  less  the  effect  of  the  residual  analy- 
ses. It  would  seem  that  in  this  experiment  the  determinations  for  the 
oxygen  were,  even  in  the  short  periods,  extremely  satisfactory. 


.  —  Record  of  Oxygen  in  Ventilating  Air  Current. 

Alcohol  check  experiment,  April  6-7,  1905. 


Date. 

Period. 

(a) 

Total 
amount 
in  cham- 
ber at 
end  of 
period. 

Gain  (+)  or 
loss(—  )  during 
period. 

M 

Amount 
admitted 
to  cham- 
ber from 
cylinder. 

<«) 

Corrected 
amount 
used  in 
combus- 
tion. 
d-c. 

00 

Required 
by 
theory. 

Or) 

Ratio  of 
amount 
found  to 
amount 
required. 
<-=-/. 

<*) 
Volume. 

(g 

Weight. 
b  -i-  0.7. 

April  6 
Do. 
Do. 
April  7 

Preliminary  

Liters. 
911.26 
927.02 
951-95 
956.24 

Liters. 

+  15.76 
+  24-93 
+    4-29 

Grams. 

+  22.51 
+  35-61 
+    6.13 

Grams. 

161.86 
242.70 
437.22 

Grams. 

139-35 
207.09 
431.09 

Grams. 

138.9° 
204.56 

426.33 
769.79 

Per  cent. 
100.3 

IOI.2 

101.  1 

First  

Second  

Third          

Total  

777-53 

IOI.O 

In  the  discussion  of  the  tests  of  accuracy  of  the  complete  apparatus, 
i. «?.,  the  respiration  calorimeter  taken  as  a  whole,  the  heat-measuring 
ability  of  the  apparatus  must  also  be  shown,  and  in  Table  4,  on  page  176, 
we  have  a  complete  statement  of  the  accuracy  of  the  ' '  respiration  calo- 
rimeter ' '  in  measuring  not  only  the  chemical  factors — carbon  dioxide, 
water  vapor,  and  oxygen — but  also  the  heat.  The  table  referred  to 
gives  a  summary  of  all  the  results  of  this  particular  experiment. 


106  A    RESPIRATION   CALORIMETER. 


THE  CALORIMETER  SYSTEM  AND  MEASUREMENT  OF  HEAT. 

This  section  deals  with  that  portion  of  the  respiration  calorimeter 
which  is  involved  in  the  calorimetric  measurements.  It  has  been  ex- 
plained (p.  4)  that  the  arrangements  for  measuring  respiratory  products 
aud  those  for  measuring  heat  are  intimately  combined  in  the  same 
apparatus.  In  this  description,  however,  the  calorimeter  will  be  con- 
sidered for  the  most  part  as  if  it  were  independent  of  the  respiration 
apparatus,  though  in  a  few  instances  it  will  be  convenient  to  refer,  for 
more  detail,  to  what  has  already  been  described. 

GENERAL   PRINCIPLE   OF  THE   CALORIMETER. 

As  a  device  for  measuring  heat,  the  apparatus  here  described  may  be 
designated  a  constant  temperature,  continuous-flow  water  calorimeter. 
It  is  so  devised  and  manipulated  that  gain  or  loss  of  heat  through  the 
walls  of  the  chamber  is  prevented,  and  the  heat  generated  within  the 
chamber  can  not  escape  in  any  other  way  than  that  provided  for  carry- 
ing it  away  and  measuring  it.  A  small  part  of  the  total  quantity  leaves 
the  chamber  as  latent  heat  of  water  vapor  in  the  air  current  of  the 
respiration  apparatus,  but  the  larger  part  is  sensible  heat  absorbed  by  a 
current  of  cold  water  passing  through  a  coil  of  pipe  within  the  chamber. 
By  regulating  the  temperature  and  rate  of  flow  of  this  current  of  water, 
the  rate  at  which  the  heat  is  absorbed  may  be  controlled  in  accordance 
with  that  at  which  it  is  generated  within  the  chamber,  and  thus  the 
temperature  of  the  chamber  may  be  kept  constant. 

The  quantity  of  heat  carried  out  of  the  chamber  as  latent  heat  of  water 
vapor  is  determined  from  the  quantity  of  water  vapor  removed  from  the 
air  current  and  the  latent  heat  of  vaporization  of  water.  The  quantity 
of  heat  absorbed  and  removed  by  the  water  current  is  determined  from 
the  quantity  of  water  passing  through  the  coil,  its  increase  in  tempera- 
ture, and  the  specific  heat  of  water  at  different  temperatures.  Theo- 
retically the  sum  of  these  two  quantities  of  heat  thus  determined  should 
equal  the  total  generated  within  the  chamber,  but  in  actual  experiments 
with  man  various  corrections,  such  as  heat  gained  or  lost  by  articles  sent 
into  or  brought  out  of  the  chambers,  etc.,  must  also  be  taken  into 
account. 

The  things  to  be  especially  considered  in  this  discussion,  then,  are 
the  arrangements  for  preventing  gain  or  loss  of  heat  through  the  walls 
of  the  chamber  and  the  arrangements  for  bringing  heat  away  from  the 
chamber  and  measuring  it.  In  the  description  of  these  many  subordinate 
related  topics  must  also  be  discussed. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT  OP   HEAT.       107 
THE   CALORIMETER   CHAMBER. 

The  dimensions  of  the  chamber  and  its  construction  of  metal  have 
been  given  in  the  discussion  of  the  respiration  apparatus  (p.  12).  The 
walls,  ceiling,  and  floor  of  the  chamber  are  of  sheet  copper,  polished 
on  the  inner  surface.  Copper  offers  many  advantages  as  a  metal  surface 
for  the  interior  of  the  calorimeter  chamber,  because  it  will  take  a  high 
polish,  thus  aiding  in  the  distribution  of  heat  by  reflection,  and  it  con- 
ducts heat  rapidly,  tbereby  tending  to  equalize  local  differences  in 
temperature.  As  a  further  aid  in  the  reflection  and  distribution  of  heat 
and  equalization  of  temperature,  the  four  upright  corners  of  the  chamber 
are  rounded.  These  features  are  of  particular  importance  in  the  matter 
of  determining  changes  in  temperature  of  the  walls,  which  is  funda- 
mental to  the  prevention  of  the  gain  or  loss  of  heat  through  the  walls, 
as  explained  beyond. 

Outside  the  copper  walls  of  the  chamber  and  concentric  with  them, 
but  separated  by  an  air-space  of  7.6  cm.,  corresponding  to  the  width 
of  the  wooden  framework  by  which  the  copper  walls  are  supported,  is 
another  metal  covering,  the  purpose  of  which  will  be  described  later. 
For  this  covering  the  cheaper  metal,  zinc,  is  very  satisfactory.  Sheets 
of  zinc  (Brown  &  Sharpe  gage  25),  each  3  by  7  feet  and  weighing  14 
pounds,  were  used  in  this  construction.  Since  this  covering  need  not 
be  airtight,  the  joints  were  soldered  only  at  convenient  places,  and 
the  zinc  is  nailed  to  the  wooden  framework  between  the  two  layers  of 
metal.  There  are,  however,  no  apertures  large  enough  to  disturb  the 
' '  dead  air ' '  in  the  space  between  the  zinc  and  the  copper. 

WOODEN  WALLS   SURROUNDING  THE   CHAMBER. 

To  protect  the  calorimeter  chamber  against  fluctuations  in  the  tem- 
perature of  the  calorimeter  laboratory,  and  especially  to  provide  op- 
portunity for  controlling  the  temperature  of  the  metal  walls  in  the 
manner  described  beyond,  there  are  two  concentric  coverings  of  wood 
completely  surrounding  it,  with  an  air-space  of  7  cm.  between  the  zinc 
wall  and  the  inner  wooden  partition  and  a  corresponding  space  between 
this  and  the  outer  wooden  covering.  This  construction  is  equivalent 
to  a  double-walled  wooden  house,  into  which  the  calorimeter  chamber 
is  inserted.  The  details  of  the  construction  follow,  reference  being 
made  to  the  horizontal  cross-section  in  figure  8  and  the  end  and  side 
vertical  cross-sections  in  figures  23  and  24. 

At  each  corner  of  the  house,  between  the  two  wooden  walls,  an  up- 
right (b,  b,  and  c,  c,  in  fig.  8)  extends  from  floor  to  ceiling  of  the  labo- 
ratory, thus  providing  rigid  supports.  As  seen  in  figure  8,  the  two 


108  A    RESPIRATION   CALORIMETER. 

uprights  at  one  end  (6,  b}  are  grooved  to  fit  the  inner  walls  ;  those  at 
the  other  end  (c,  c)  are  rectangular  in  cross-section.  All  four  up- 
rights are  well  painted  to  prevent  absorption  of  moisture  and  conse- 
quent warping,  such  precaution  being  especially  necessary  because  of 
the  location  of  the  laboratory  in  the  basement  of  a  stone  building. 

Extending  between  these  uprights  in  both  directions,  at  the  top  and 
bottom  of  the  structure,  are  joists  ;  those  extending  across  the  shorter 
dimension  are  shown  in  cross-section  in  figure  24  (a,  a  and  b,  £),  and 
those  running  lengthwise  in  figure  23  {a,  a  and  b,  £) .  These  eight  joists 
and  the  four  uprights  form  a  rigid  support  for  the  wooden  walls. 
Like  the  two  uprights  b,  b,  shown  in  figure  8,  the  two  joists  a,  a,  shown 
in  figure  24,  are  grooved  to  receive  the  inner  wooden  partition. 

The  floor  of  the  outer  wooden  structure  rests  upon  two  pieces  of 
cedar  15  by  15  cm. ,  shown  in  cross-section  (c,  c,  in  fig.  24),  which  are  laid 
directly  upon  the  laboratory  floor.  These  hold  the  ends  of  the  floor  of 
the  outer  casing  firmly  against  the  lower  edges  of  the  joists  a  and  b.  In 
addition  to  these  there  are  nine  large  blocks  (</,  d,  d,  in  figs.  23  and  24) 
placed  under  the  cleats  of  the  floor  at  the  points  where  the  weight  of 
the  calorimeter  is  supported ;  that  is,  under  the  castors  on  which  it  stands. 
Between  the  floor  ot  the  outer  and  that  of  the  inner  wooden  structure 
are  smaller  blocks  (<r,  e,  fig.  23,  and  <?,  <?,  <?,  fig.  24),  upon  which  rest 
the  cleats  of  the  inner  wooden  floor,  these  cleats  being  directly  under 
the  castors. 

All  other  parts  of  the  walls,  floors,  and  ceilings  of  both  inner  struct- 
ures are  securely  fastened  to  the  joists  and  uprights  above  described, 
but  in  such  manner  that  when  necessary  they  may  be  easily  removed 
so  as  to  render  all  parts  of  the  outside  of  the  calorimeter  accessible. 
To  facilitate  the  removal,  each  wall,  ceiling,  or  floor  is  constructed  as  a 
panel,  from  matched  hard  pine,  screwed  together  with  a  number  of 
cleats  and  battens,  as  illustrated  in  figures  23  and  24.  The  outer  panels 
are  provided  with  metal  handles  sunk  into  the  wood  for  convenience 
in  removing  them.  In  spite  of  the  large  size  of  the  panels  (the  smallest 
being  1.62  by  2.24  meters),  none  of  them  shows  evidence  of  warping 
after  having  been  used  over  three  years.  Matched  boards  were  used  to 
avoid  cracks,  which  would  afford  opportunity  for  the  diffusion  of  air. 

Of  the  eight  panels  forming  the  sides  and  ends  of  the  two  wooden 
structures,  six  are  readily  removable.  The  other  two,  namely,  those 
at  the  end  in  which  the  window  is  built,  may  also  be  removed  if  neces- 
sary, but  to  take  out  the  outer  panel  in  this  end  involves  considerable 
trouble  in  disconnecting  apparatus  adjacent  to  it  on  the  outside.  The 
occasions  for  removing  this  panel,  however,  are  very  rare.  Even  in 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT  OF   HEAT.       109 


} 


10 


I 


FIG.  a?.— Vertical  Cross-Section  of  Calorimeter  Chamber  through  the  end.  The  chamber  consists 
of  four  concentric  shells,  two  inner  ones  of  metal  and  two  outer  ones  of  wood.  The  air-spaces 
and  the  wooden  separators  dividing  the  inner  air-space  (/,./, /,/,./,/),  as  well  as  the  castors  on 
which  the  metal  chamber  rests,  are  also  shown. 


no 


A   RESPIRATION   CALORIMETER. 


case  of  an  accident  to  some  of  the  connections  between  the  two  panels 
at  this  end,  it  is  more  convenient  to  remove  the  two  panels  from  the 
rear  end,  withdraw  the  metal  chamber,  and  then  take  out  the  inner 
panel  from  the  front  end.  Under  all  ordinary  circumstances  the  two  rear 
panels  are  the  only  ones  removed.  A  view  with  these  two  panels  taken 
out  and  resting  against  the  side  of  the  house  is  shown  in  figure  25. 


FIG.  24. — Vertical  (side)  Cross-Section  of  Calorimeter  Chamber.    This  view  shows  openings  for 
window  and  food  aperture,  position  of  castors,  wooden  separators  (f,f,f,f),  and  panels. 

The  space  between  the  floor  of  the  laboratory  and  that  of  the  outer 
wooden  casing  is  inclosed  by  a  baseboard  or  mopboard  on  all  four  sides. 
A  similar  board  extends  around  the  top  of  the  calorimeter  and  con- 
fines the  air  in  the  space  between  the  ceiling  of  the  outer  wooden  casing 
and  that  of  the  laboratory.  All  of  these  boards,  both  top  and  bottom, 
may  be  easily  removed. 


I 


To  face  page  110. 


FIG.  25.— Rear  View  of  Calorimeter  Chamber  showing  the  two  panels  removed  and  the  iron  tracks 
on  which  Chamber  is  rolled.  The  water-cooling  pipes  stretch  horizontally  across  end  of  calo- 
rimeter. White  porcelain  knobs  are  usedfor  suspending  the  heating  wires.  The  food  aperture 
is  seen  in  center  of  Chamber. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT  OF   HEAT.       Ill 
AIR-SPACES  AND   HEAT    INSULATION. 

From  the  above  description  and  the  illustrations  in  figures  8,  23,  and 
24,  it  is  seen  that  the  calorimeter  chamber  and  its  wooden  house  con- 
sist of  a  series  of  concentric  shells,  the  inner  one  of  copper  being  envel- 
oped by  a  zinc  shell  and  two  wooden  shells,  with  the  different  shells 
separated  by  air-spaces.  The  important  feature  of  this  construction 
is  the  insulation  against  heat.  Between  the  outer  and  inner  wooden 
structures  is  the  "outer"  air-space,  and  between  the  inner  wooden 
casing  and  the  zinc  wall  is  the  "  inner  "  air-space.  Between  the  two 
metal  walls  is  still  a  third  air-space.  The  confined  dead  air  in  these 
spaces  is  an  excellent  heat  insulator.  To  render  the  air  in  these  spaces 
as  nearly  ' '  dead  ' '  as  possible,  the  panels  are  made  very  tight  by  the  use 
of  matched  boards,  as  above  described,  and  at  the  edges  are  fitted  very 
closely  to  prevent  escape  or  entrance  of  air.  Further  insulation  against 
heat  is  provided  by  coating  both  surfaces  of  the  inner  wooden  casing 
and  the  inner  surface  of  the  outer  casing  with  asbestos  paper.  This 
was  applied  to  the  surface  of  the  panels  by  means  of  the  ordinary  paste 
used  by  paperhangers,  and  it  has  shown  no  tendency  to  become  loose  ; 
the  fibrous  nature  of  the  asbestos  furnishes  a  very  good  surface  for 
adhesion. 

It  will  be  seen  from  the  figures  showing  cross- sections  that  the  up- 
rights and  joists  of  the  framework  divide  the  outer  air-space  into  six 
separate  sections — top,  bottom,  and  four  sides.  The  inner  air-space 
surrounding  the  zinc  wall  is  continuous  so  far  as  the  construction  of 
the  wooden  casing  is  concerned.  It  has  been  found  desirable,  how- 
ever, in  connection  with  the  arrangements  for  controlling  the  temper- 
ature of  this  space,  described  later,  to  divide  it  into  sections.  This  is 
accomplished  by  means  of  wooden  strips,  nearly  as  wide  as  the  space 
between  the  metal  and  wooden  walls,  running  parallel  to  the  floor  and 
the  ceiling,  one  edge  of  the  strip  being  attached  to  the  inside  of  the 
inner  wooden  wall  and  the  other  edge  being  provided  with  a  felt  flap 
that  rests  against  the  zinc  wall.  The  strips  are  attached  to  the  wooden 
walls  by  means  of  hinges,  so  that  they  may  be  turned  up  out  of  the 
way  when  the  calorimeter  chamber  is  to  be  rolled  out  of  the  wooden 
house.  The  strips  are  shown  (/,  /,  /,  /)  in  figures  23  and  24,  and 
may  also  be  seen  in  figures  30  and  3 1 .  The  space  above  the  top  of  the 
chamber  is  divided  into  one  section  by  the  strips  at  the  upper  edges, 
and  that  below  the  floor  of  the  chamber  is  likewise  separated  into  an- 
other section  by  strips  at  the  lower  edges.  The  space  surrounding 
the  four  sides  of  the  chamber  is  divided  into  two  sections  by  strips  half 
way  between  the  top  and  the  bottom. 


113  A    RESPIRATION   CALORIMETER. 

FACILITIES   FOR   REMOVING   METAL   CHAMBER. 

In  case  of  accident  to  any  part  of  the  outside  of  the  calorimeter 
chamber  it  is  necessary  to  have  easy  access  to  that  part.  The  partic- 
ular form  of  construction  above  described  was  adopted  to  secure  ready 
accessibility  to  all  parts  of  the  apparatus,  as  already  explained. 

The  calorimeter  chamber,  exclusive  of  any  fittings,  weighs  605 
pounds.  To  facilitate  withdrawing  the  chamber  from  the  wooden 
casing,  six  large  castors,  three  on  each  side,  are  fastened  to  the  bot- 
tom. These  castors  move  in  iron  tracks  laid  on  the  floor  of  the  inner 
wooden  structure,  the  tracks  being  of  the  grooved  iron  commonly  used 
in  bridge  construction.  The  raised  edges  serve  as  guides  to  the  wheels. 
Beyond  the  inner  wooden  floor  each  track  is  continued  along  a  stiff 
joist,  the  end  of  which  is  cut  so  as  to  fit  over  the  wooden  casing  of  the 
calorimeter  and  thus  allow  the  ends  of  the  track  to  come  together  and 
form  a  continuous  passage  for  the  wheels  of  the  calorimeter.  The 
joists  are  laid  on  the  floor  of  the  laboratory  and  when  not  in  use  are 
removed.  When  supporting  the  calorimeter  they  are  held  rigidly  up- 
right by  a  cross-piece  at  the  outside  ends.  Figure  25  shows  the  tracks 
extending  from  the  wooden  casing,  and  figure  29  shows  the  calorimeter 
rolled  out  upon  them. 

METHODS   OF   PREVENTING   GAIN   OR   LOSS   OF   HEAT   TO   CHAMBER. 

It  has  been  stated  that  the  heat  generated  within  the  chamber  can 
not  escape  from  it  except  by  the  means  provided  for  carrying  it  away 
and  measuring  it.  In  order  that  this  shall  be  the  case  and  also  that  the 
amount  thus  measured  shall  include  only  that  produced  within  the 
chamber  and  shall  not  be  augmented  by  heat  from  external  sources, 
there  must  be  no  gain  or  loss  of  heat  through  the  metal  walls,  the 
openings  in  the  walls,  or  the  air  current.  The  arrangements  for  pre- 
venting gain  or  loss  of  heat  by  these  channels  are  here  described. 

PREVENTION  OF  GAIN  OR  Loss  THROUGH  THE  METAL  WALLS. 

If  the  zinc  wall  were  colder  than  the  copper  there  would  be  an  out- 
ward flow  of  heat,  i.  e. ,  a  loss,  and  if  it  were  warmer  there  would  be  an 
inward  flow  or  gain.  To  prevent  the  passage  of  heat  in  either  direc- 
tion, or,  more  strictly,  to  provide  that  the  small  quantity  that  may  pass 
one  way  shall  be  exactly  counterbalanced  by  an  equal  quantity  in  the 
other  direction,  the  temperature  of  the  zinc  is  regulated  in  accordance 
with  that  of  the  copper.  This  is  accomplished  by  heating  or  cooling 
the  air-space  surrounding  the  zinc  walls  as  necessary,  according  to 
whether  the  zinc  is  colder  or  warmer  than  the  copper. 

First  of  all,  then,  it  is  necessary  to  detect  differences  between  the 
temperature  of  the  copper  and  that  of  the  zinc  wall. 


THE   CALORIMETER  SYSTEM   AND   MEASUREMENT  OP   HEAT.       113 
THE  THERMO-ELECTRIC  ELEMENTS. 

Differences  in  the  temperatures  of  the  zinc  and  the  copper  walls  are 
indicated  by  a  current  of  electricity  generated  by  thermal  junctions1  of 
iron  and  German- silver  wire  inserted  between  the  metal  walls  and  con- 
nected with  a  reflecting  galvanometer.  There  are  in  all  304  pairs  of 
such  junctions  distributed  throughout  the  metal  walls  in  groups,  each 
group  containing  four  pairs  of  junctions  and  comprising  what,  for  con- 
venience, is  termed  an  element.  The  thermo-electric  element  used  in 
this  calorimeter  is  illustrated  in  figure  26. 

Construction  of  the  element. — Bach  element  consists  of  four  pairs  of 
j  unctions  of  iron  and  German-silver  wires,  inserted  in  grooves  in  a  wooden 
cylinder.  The  iron  wire  consists  of  "soft,  bright  Bessemer  steel  wire, 
Washburn  &  Moen  gage  No.  19."  The  other  is  so-called  nickel 
German-silver  wire,  18  per  cent,  Brown  &  Sharpe  gage  No.  18. 
Four  short  pieces  of  the  iron  wire  were  joined  with  silver  solder,  by 
means  of  a  blow-pipe,  to  three  pieces  of  German-silver  wire  of  the 
same  length  and  two  pieces  somewhat  longer,  and  then  bent  in  the 
manner  shown  in  figure  26,  in  which  the  iron  wire  is  represented  by 
the  solid  black  line.  They  were  then  crowded  into  slots  in  a  short 
wooden  rod  made  of  thoroughly  seasoned,  straight-grained,  hard  maple. 
As  is  seen  in  figure  27,  one  of  the  long  German-silver  wires  is  doubled 
on  itself  and  brought  out  parallel  to  the  other.  By  this  arrangement 
there  are  four  soldered  unions  of  iron  and  German- silver  at  each  end 
of  the  wooden  rod.  The  ends  of  the  German-silver  wire  are  fastened 
to  copper  wires  leading  to  the  galvanometer.  The  completed  element, 
as  above  described,  is  finally  boiled  for  some  time  in  paraffin  to  expel 
moisture  and  insure  perfect  electrical  insulation. 

Method  of  installing  elements. — The  method  of  installing  the  elements 
in  the  metal  walls  is  illustrated  in  figure~28. 

The  base  of  a  copper  thimble,  15  mm.  in  diameter  and  16  mm.  deep, 
having  straight  sides,  is  soldered  to  the  outer  surface  of  the  copper 
calorimeter  shell,  /.  <?.,  in  the  space  between  the  zinc  and  the  copper. 
Directly  opposite  this  thimble  in  the  zinc  wall,  a  copper  ring,  15  mm. 
internal  diameter  and  26  mm.  long,  is  soldered  in  such  a  position  that 
it  extends  13  mm.  outside  of  the  zinc  wall.  The  thermo-electric  ele- 
ment is  then  slipped  through  the  ring  soldered  in  the  zinc  wall,  and 
the  inner  end  of  the  element  inserted  into  the  thimble  soldered  to  the 

1  The  use  of  thermal  junctions  for  this  purpose  was  originally  suggested  by  Dr. 
E.  B.  Rosa.  The  use  of  this  principle  in  calorimetric  work  has  been  attended  with 
such  excellent  success  that  it  is  retained  here,  although  the  form  of  element  has 
been  modified.  The  present  form  was  devised  by  Mr.  ().  S.  Blakeslee,  formerly 
mechanician  of  Wesleyan  University. 

SB 


A   RESPIRATION   CALORIMETER. 


copper  wall.  The  length  of  the  wooden  cylinder  and  of  the  wires  is 
such  that  when  one  end  is  thus  inserted  in  the  thimble  the  junctions  at 
the  other  end  are  exactly  in  the  plane  of  the  zinc  wall.  The  element 
is  held  in  place  by  a  cork  firmly  inserted  in  the  outer  aperture  of  the 
ring  in  the  zinc  wall.  The  ends  of  the  two  long  German-silver  wires 
that  lead  to  the  junctions  are  passed  through  holes  in  the  cork,  which 
are  far  enough  apart  to  insure  insulation  between  the  two  German- 
silver  wires,  and  likewise  far  enough  from  the  edge  of  the  cork  to  in- 
sure insulation  between  these  wires  and  the  copper  ring  soldered  into 
the  zinc  wall.  The  ends  of  the  thermal  junctions  are  far  enough  below 


Fig.  26. 


Fig.  27. 


Fig.  28. 


FIG.  26. — Thermo-Electric  Element.  Iron  wires  (represented  by  black  line)  and  German-silver 
wires  are  soldered  with  silver  solder,  making  a  series  of  four  junctions  at  each  end. 

FIG.  27.— Thermo-Electric  Element  Mounted  on  Wooden  Rod.  The  iron  and  German-silver  wires 
are  pressed  well  into  slits  in  the  sides.  The  two  projecting  wires  are  for  connections. 

FIG.  28. — Method  of  Installing  the  Thermo-Electric  Elements  in  the  Metal  Walls.  A  short  tube 
soldered  in  the  zinc  wall  holds  the  element  in  place. 

the  outer  surface  of  the  wooden  cylinder  to  prevent  any  possible  elec- 
trical contact  with  either  the  copper  thimble  on  the  copper  wall  or  the 
ring  on  the  zinc  wall,  while  the  small  air-gap  does  not  seem  to  retard 
unduly  the  passage  of  heat  from  the  copper  or  zinc  wall  to  the  junc- 
tions. In  this  position  a  junction  is  able  to  take  up  rapidly  at  each 
end  the  temperature  of  the  corresponding  metal  wall. 

The  detection  of  differences  in  temperature  between  the  two  metal 
walls  by  means  of  the  thermal  junctions  thus  inserted  depends  upon 
the  fact  that  if  the  ends  of  the  two  kinds  of  wire  forming  the  junction 
are  unequally  heated  a  current  of  electricity  is  developed,  the  intensity  of 


THE  CALORIMETER  SYSTEM   AND   MEASUREMENT  OP   HEAT.       115 

which  is  dependent  upon  the  difference  in  temperature.  The  intensity 
of  the  current  can  be  accurately  noted  with  a  delicate  galvanometer, 
and  consequently  the  difference  in  temperature  closely  measured.  Ob- 
viously, in  the  case  of  noting  the  difference  in  temperature  between 
the  copper  and  the  zinc  walls,  it  is  necessary  not  only  that  the  thermal 
junctions  be  in  the  best  possible  thermal  contact  with  the  correspond- 
ing metal  walls,  but  also  that  there  must  be  absolutely  no  electrical 
contact  to  impair  the  accuracy  of  the  measurements.  The  grooves  in 
the  wooden  rod  are  sunk  sufficiently  deep  to  bring  the  ends  of  the 
junctions  considerably  below  the  surface  of  the  wooden  cylinder.  As 
will  be  seen  on  studying  the  method  of  installing  the  junctions,  this 
position  of  the  ends  of  the  junctions  is  necessary  to  secure  electrical 
insulation  from  the  copper  and  zinc  walls  of  the  calorimeter. 

Distribution  of  elements. — As  it  is  desired  to  keep  the  temperature  of 
the  zinc  wall  exactly  the  same  as  that  of  the  copper  wall,  the  elements 
should  be  distributed  over  the  whole  six  sides  of  the  chamber  in  such  a 
manner  that  each  one  may  assume  the  average  temperature  of  a  certain 
portion  of  the  total  area  of  metal ;  that  is,  the  elements  should  be  dis- 
tributed all  over  the  area  of  the  calorimeter  in  points  very  closely  pro- 
portional to  the  area.  As  a  matter  of  fact,  the  junctions  are  located 
about  48  cm.  apart,  and  each  exercises  the  temperature  control  of  an 
area  of  metal  about  48  by  48  cm.  The  distribution  of  the  various  ele- 
ments in  the  rear  end  of  the  chamber  is  seen  in  figure  25,  which  shows 
the  respiration  chamber  inside  the  wooden  house,  the  rear  panels  of 
which  have  been  removed.  In  this  figure  the  location  of  ten  elements 
is  distinctly  shown.  The  wires  attached  to  the  calorimeter  in  a  "  zigzag 
fashion ' '  are  connected  to  elements  at  each  point  where  the  direction 
of  the  wire  is  changed.  Only  two  elements  appear  in  the  lowest  zone, 
and  here  the  connecting  wires  do  not  take  a  zigzag  course. 

In  figure  29  a  view  of  the  distribution  of  the  elements  on  one  side  of 
the  calorimeter  is  shown.  There  are  here,  as  on  the  end  of  the  calo- 
rimeter, two  zigzag  rows  of  fourteen  elements  and  a  lower  row  of 
three  elements  in  a  straight  line.  The  number  and  distribution  of  the 
elements  on  the  wall  of  the  metal  chamber  opposite  to  that  shown  in 
figure  29  is  precisely  the  same.  Owing  to  difficulties  in  photographing 
the  apparatus,  no  figure  is  given  showing  the  distribution  of  the  eleven 
elements  on  the  top  or  the  eleven  on  the  bottom  of  the  calorimeter.  The 
nine  elements  on  the  front  end  of  the  chamber  are  shown  in  figure  30. 
There  is  also  one  additional  element  in  a  position  that  does  not  appear 
in  any  of  the  photographs.  This  makes  in  all  seventy-six  elements, 
each  containing  four  pairs  of  thermal  junctions. 


Il6  A    RESPIRATION   CALORIMETER. 

Elect*  ical  connections  of  the  elements. — As  may  be  seen  from  the  illus- 
trations in  figures  25,  29,  and  30,  all  the  elements  are  connected  in 
series.  When  the  ends  of  the  whole  system  are  connected  with  the 
galvanometer  the  deflection  obtained  is  not  that  due  to  the  current 
from  a  single  element,  but  it  is  the  resultant  of  all  the  positive  and 
negative  electro- motive  forces  of  all  the  elements.  It  is  very  essential, 
however,  to  be  able  to  determine  temperature  conditions  for  different 
sections  of  the  total  area  of  the  chamber.  It  is  conceivable,  for  ex- 
ample, that  even  while  the  zinc  and  copper  walls  at  the  ends  and  sides 
of  the  calorimeter  remain  adiabatic,  at  the  top  the  zinc  wall  may  be 
warmer  than  the  copper,  and  at  the  bottom  the  copper  wall  may  be 
warmer  than  the  zinc.  If  there  were  the  same  difference  in  tempera- 
ture in  both  cases  the  algebraic  sum  of  the  electro- motive  forces  would 
be  zero,  indicating  that  the  temperatures  of  the  zinc  and  copper  walls 
were  the  same  over  the  whole  area,  and  consequently  no  passage  of 
heat  in  either  direction,  whereas  heat  would  actually  be  passing  out 
at  the  bottom  and  entering  at  the  top. 

In  order  to  prevent  such  temperature  differences  in  local  sections  of 
the  total  area,  the  whole  system  of  elements  is  subdivided  into  groups 
corresponding  with  different  regions,  so  that  it  is  possible  to  detect  not 
only  average  temperature  differences  for  the  total  area,  but  also  local 
differences.  The  whole  surface  area  is  divided  into  four  parts,  the  top 
being  one  and  the  bottom  another.  The  upper  double  row  of  elements 
connected  by  wires  in  a  zigzag  line  comprises  the  third  division,  and 
the  lower  zigzag  row  and  the  row  in  a  straight  line  around  the  bottom 
together  form  the  fourth  division.  For  convenience  these  divisions 
are  designated  as  top,  bottom,  upper  zone,  and  lower  zone,  respectively. 
By  means  of  connecting  wires  leading  from  the  points  at  which  the 
various  sections  are  joined  together,  each  individual  section  can  be 
connected  at  will  with  the  galvanometer  and  the  temperature  differ- 
ences indicated  by  the  electro-motive  force  ascertained. 

It  will  be  seen  by  comparing  the  above  explanation  with  figure  29 
that  the  division  of  the  vertical  walls  of  the  calorimeter  in  the  two  zones 
is  not  an  equal  one,  the  upper  zone  being  much  less  in  area  than  the 
bottom.  Since,  however,  the  upper  zone  is  subject  to  much  wider 
fluctuations  in  temperature  because  of  variations  in  the  temperature 
and  exposed  surface  of  the  heat-absorbing  system,  it  is  advisable  to 
have  temperature  differences  located  in  this  small  zone  as  precisely  as 
possible. 

While  the  thermal  junctions  in  each  group  are  used  to  detect  tem- 
perature differences  between  the  copper  and  zinc  walls,  no  absolute 
measurements  of  such  differences  are  made.  In  general,  the  differences 


to  face  page  11s-i. 


i 


•-  - 
o  S 


ii 

o!  .2 


To  faoe  page  116-2. 


FIG.  30. — Front  View  of  the  Metal  Chamber  removed  from  the  wooden  casing.  Through  the 
window  opening  are  seen  a  shield  for  the  heat-absorber,  the  food  aperture  door,  and  the  chair. 
The  piping  and  wiring  on  the  inner  wooden  panels  as  well  as  the  movable  partitions  subdivid- 
ing the  inner  air-space  are  also  shown. 


THE   CALORIMETER  SYSTEM   AND   MEASUREMENT   OF   HEAT.       1 17 

are  very  small,  and  by  constantly  heating  or  cooling  the  air-space  next 
the  zinc,  as  indicated  by  the  positive  and  negative  deflections  on  the 
galvanometer,  the  temperature  of  the  zinc  itself  is  increased  or  dimin- 
ished, as  the  case  may  be,  so  that  the  temperature  of  the  two  metal  walls 
shall  always  be  very  nearly  alike. 

The  arrangements  for  heating  and  cooling  the  air-space  next  the 
zinc  wall  are  next  to  be  considered. 

HEATING   AND   COOLING  THE   AIR-SPACK. 

The  air-space  surrounding  the  zinc  wall  and  between  this  and  the 
inner  wooden  casing  has  been  described  (p.  1 1 1 ) ,  and  it  has  been  shown 
that  this  space  is  divided  by  narrow  strips  into  four  sections,  corre- 
sponding with  the  top  and  bottom  of  the  chamber  and  the  upper  and 
lower  halves  of  the  walls.  (See  fig.  23.)  Comparing  this  with  the  ex- 
planation in  the  paragraphs  j  ust  above,  it  will  be  seen  that  these  divisions 
of  the  air-spaces  correspond  with  the  areas  covered  by  the  different 
groups  of  elements  into  which  the  whole  system  of  thermo-electric 
elements  is  subdivided.  The  devices  here  described  for  heating  and 
cooling  the  air-spaces  are  arranged  so  that  the  different  sections  of  the 
space  may  be  heated  or  cooled  independently.  In  other  words,  pro- 
vision is  made  for  determining  temperature  differences  in  different  sec- 
tions of  the  surface  area  of  the  calorimeter,  and  also  for  heating  or 
cooling  the  corresponding  areas  in  the  zinc  wall  as  may  be  indicated. 
Thus,  it  is  possible  to  heat  one  space  and  cool  the  adjoining  space  at 
the  same  time. 

Heating  circuits. — For  heating  the  air-spaces  a  current  of  electricity 
is  passed  through  a  circuit  of  German-silver  wire,  each  separate  space 
having  its  individual  heating  circuit.  The  wire  is  threaded  through 
porcelain  rings  at  the  ends  of  each  wooden  panel  and  wound  once 
around  porcelain  knobs  at  three  different  points  in  the  length  of  the 
panel.  By  this  arrangement  the  wire  is  firmly  held  in  place,  and  even 
during  the  slight  sagging  due  to  expansion  when  heated,  is  prevented 
from  coming  in  contact  with  the  metal  wall  of  the  chamber.  The 
white  porcelain  knobs  or  insulators  on  which  the  heating  wires  are 
strung  are  readily  seen  in  figures  25,  29,  30,  and  especially  in  figure  31. 

The  wire  itself  is  so  fine  that  it  is  hardly  discernible  in  some  of  the 
figures,  being  quite  plainly  seen,  however,  in  figure  30.  In  the  upper 
and  lower  side  spaces  the  current  flows  around  all  four  sides  at  the 
same  time.  The  wires  are  attached  to  the  wooden  walls,  however,  in 
such  manner  that  they  may  be  disconnected  at  the  corners  when  the 
panels  are  to  be  removed.  The  heating  circuits  for  the  top  and  bot- 
tom sections  are  attached  in  one  unbroken  wire  stretched  continuously 
back  and  forth  across  each  of  the  respective  panels. 


Il8  A    RESPIRATION   CALORIMETER. 

Each  heating  circuit  is  connected  with  a  variable  resistance  and  a 
rheostat  on  the  observer's  table.  It  is  possible  to  cut  out  any  or  all 
of  the  resistance  and  cause  varying  amounts  of  electricity  to  pass 
through  the  circuit  of  wire  in  the  air-space,  thus  controlling  its  heating 
effect.  The  electrical  method  of  heating  a  large  air-space  is  ideal,  in- 
asmuch as  the  heat  is  evenly  distributed  all  through  the  air-space  and 
liberated  simultaneously  at  all  points.  Furthermore,  the  amount  of 
heat  which  can  thus  be  liberated  is  instantly  controlled  with  the  greatest 
accuracy  by  varying  the  external  resistances. 

The  variable  resistance  here  used  consists  of  a  series  of  seven  coils  of 
German-silver  wire  wound  on  a  corrugated  sheet-iron  pipe  (galvanized 
conductor  pipe)  which  has  been  covered  with  asbestos  paper.  There 
are  in  all  nine  heating  circuits  used  for  temperature  control  about  the 
calorimeter,  four  for  the  inner  air-space,  four  for  the  outer  air-space, 
and  one  to  heat  the  ventilating  current  of  air  as  it  enters  the  chamber, 
each  of  which  is  connected  with  the  rheostat  and  has  its  variable  resist- 
ance. The  nine  variable  resistances  are  laid  side  by  side  under  the 
calorimeter  in  the  space  between  the  laboratory  floor  and  the  outer 
bottom  panel.  As  the  floor  of  the  laboratory  is  always  cold,  the  extra 
heat  developed  in  these  resistance  coils  in  a  measure  counteracts  the 
cold  floor  and  aids  in  warming  the  outer  bottom  dead-air  space. 

Cooling  circuits. — Means  for  cooling  the  air-spaces  are  as  essential  as 
those  for  heating  them.  Unfortunately,  there  is  no  such  ideal  method 
for  cooling  as  for  heating  an  air-space.  The  best  method  available  is 
that  depending  upon  the  passage  of  cold  water  through  a  small  pipe 
which  is  suspended  in  the  air-space  parallel  to  the  wires  of  the  elec- 
trical heating  circuit.  (See  figs.  25,  30,  and  31.)  Water  from  the  city 
main,  which  has  a  temperature  varying  from  6°  in  winter  to  16°  or  17° 
in  summer,  is  caused  to  flow  through  small  pipes  (one-eighth  inch)  in 
the  air-space.  The  cold  water  absorbs  the  heat  and  thus  cools  the  air 
rapidly,  and  as  a  result  the  zinc  wall  is  cooled. 

Heretofore  iron  pipe  has  been  used  for  the  cooling  circuits,  but  as  it 
rusts  easily  and  so  is  liable  to  clog,  brass  pipe  is  being  substituted. 

The  cooling  system  in  the  top  space  and  that  in  the  bottom  space 
are  individual  units,  in  which  the  water  enters  at  one  end,  circulates 
around  the  numerous  bends  in  the  pipe,  and  goes  out  at  a  point  close 
to  where  it  enters.  With  the  cooling  circuits  for  the  upper  and  lower 
zones,  on  the  other  hand,  it  is  necessary  to  make  arrangements  for  dis- 
connecting the  piping  when  the  calorimeter  is  to  be  withdrawn.  The 
position  of  the  pipes  across  the  rear  end  of  the  calorimeter  is  shown  in 
figure  25.  These  pipes  are  attached  to  elbows  connecting  with  the 
pipes  on  the  side  panels  by  means  of  a  brass  union  at  each  end.  By  dis- 


To  face  page  118. 


FIG.  31.— Details  of  Interior  of  Wooden  Casing,  showing  cooling  pipes,  electrical  heating  wires,  partitions 
for  subdividing  inner  air-space  and  openings  in  the  case  to  correspond  to  the  windows,  air-pipes,  and 
water-pipes.  The  tracks  on  which  the  metal  chamber  stands  are  seen  on  the  floor. 


f 

THE   CALORIMETER  SYSTEM   AND   MEASUREMENT   OF   HEAT.       1 19 

connecting  the  unions,  each  pipe  can  be  sprung  a  little  and  thus  readily 
removed. 

The  heat-absorbing  capacity  of  the  mass  of  water  in  the  pipe  is  very 
great,  much  more  so  than  that  of  the  metal  of  the  pipe  itself,  since  the 
specific  heat  of  water  is  about  ten  times  that  of  the  pipe.  Consequently, 
in  order  to  secure  a  quick  and  easily  controlled  heat  absorption,  it  is 
necessary  to  provide  for  the  rapid  draining  out  of  the  water  in  the  cool- 
ing system.  As  the  water  leaves  the  valve  connected  with  the  water 
main  it  traverses  the  section  of  the  pipe  with  which  the  valve  is  con- 
nected. When  the  valve  is  shut  off  a  check-valve  attached  to  an  upright 
section  of  pipe  (see  fig.  37)  opens,  allowing  air  to  enter.  As  each  section 
is  purposely  piped  in  such  a  manner  as  to  allow  a  free  outflow  of  the 
water,  the  water  in  the  pipes  quickly  drains  out,  and  thus  the  cooling 
effect  is  much  more  rapidly  arrested. 

TEMPERATURE  REGULATIONS  IN  THE  OUTER  AIR-SPACE. 

The  temperature  regulation  of  the  air-space  next  the  zinc  wall  is 
affected  by  the  fluctuations  in  temperature  inside  the  metal  chamber, 
and  also,  in  spite  of  the  insulating  of  the  wooden  walls  papered  with 
asbestos,  by  the  temperature  of  the  calorimeter  laboratory.  The  outer 
air-space,  i.  e.,  that  between  the  inner  and  outer  wooden  casings, 
dampens  the  effect  of  sudden  changes  in  temperature  of  the  calorimeter 
laboratory,  but  to  aid  in  regulation  provision  is  made  to  heat  and  cool 
the  outer  air-spaces  at  will.  The  heating  and  cooling  circuits  in  these 
spaces  are  of  exactly  the  same  nature  as  those  described  above  for  the 
inner  spaces,  except  that,  since  the  delicate  control  of  the  temperature 
in  the  outer  air-space  is  much  less  important,  no  provision  is  made  for 
draining  the  water  out  of  the  water-pipes  installed  in  this  air-space. 

The  necessity  for  heating  or  cooling  the  outer  spaces  is  likewise 
determined  by  deflections  on  a  galvanometer  connected  with  a  series  of 
thermo-electric  elements.  These  are  inserted  in  the  inner  wooden  walls, 
one  end  of  the  junctions  being  in  the  inner  and  the  other  end  in  the  outer 
space.  There  are  fifty-four  such  elements  (containing  each  four  pairs 
of  thermal  junctions)  distributed  throughout  the  six  inner  panels  at 
equal  distances  from  each  other,  so  as  to  assume  more  nearly  the  average 
temperature  of  the  air-space.  The  black  irregular  line  (not  to  be  con- 
fused with  the  series  of  parallel  black  iron  pipes)  on  the  right-hand 
inner  wall  in  figure  31  shows  the  method  of  connecting  these  elements. 
Along  the  upper  portion  of  the  panel,  running  parallel  to  the  iron  pipes, 
is  one  straight  row  of  four  elements.  A  somewhat  different  view  is 
given  in  figure  30,  and  the  distribution  on  the  inner  rear  panel  may  be 
seen  in  figure  25,  in  which  the  panel  is  removed  and  standing  at  the  right. 


120  A   RESPIRATION    CALORIMETER. 

• 

As  with  those  on  the  metal  chamber  itself,  the  thermo-electric  ele- 
ments in  this  system  are  also  subdivided  into  four  sections — the  top, 
upper  zone,  lower  zone,  and  bottom. 

On  the  chamber  itself  the  different  members  of  each  group  of  ele- 
ments are  permanently  connected  in  series,  but  with  the  system  here 
considered  it  is  necessary  to  break  connections  in  the  upper  and  lower 
zones  when  removing  the  end  panels  and  withdrawing  the  chamber. 
The  connections  between  the  elements  in  the  top  panel  and  in  the  bottom 
panel  are  in  no  wise  disturbed  by  withdrawing  the  metal  chamber  ;  only 
the  wires  joining  the  elements  of  the  upper  and  lower  zones  on  the  side 
panels  with  the  elements  of  the  upper  and  lower  zones  on  the  end  panel 
must  be  disconnected.  These  connections  are  made  by  nuts  or  binding 
posts. 

GAIN  OR  Loss  OF  HEAT  THROUGH  OPENINGS  IN  THE  CHAMBER. 

The  various  openings  through  the  metal  walls  of  the  chamber  have 
been  described  in  detail  (p.  13).  The  nature  of  some  of  these,  or  at 
least  of  the  objects  for  which  they  are  provided,  precludes  the  passage 
of  any  appreciable  quantity  of  heat  in  either  direction.  In  the  case  of 
two  of  them,  however,  namely,  the  window  in  the  front  and  the  food 
aperture  in  the  rear,  there  is  a  possibility  of  gain  or  loss  of  heat,  de- 
pending upon  differences  between  the  temperature  of  the  air  within  the 
chamber  and  that  of  the  calorimeter  laboratory.  In  fact,  that  there 
may  be  under  certain  circumstances  appreciable  interchange  of  heat 
through  these  two  openings  has  been  proved  by  a  number  of  experi- 
ments in  which  the  temperature  of  the  calorimeter  laboratory  was 
markedly  different  from  that  of  the  chamber.  To  prevent  such  inter- 
change of  heat  it  has  been  found  necessary,  therefore,  to  keep  the 
temperature  of  the  laboratory  as  nearly  as  possible  the  same  as  that 
within  the  chamber. 

To  this  end  a  mercury  thermometer  is  hung  inside  the  calorimeter 
chamber  with  its  bulb  opposite  the  center  of  the  window,  and  a  similar 
thermometer,  with  exactly  the  same  corrections,  is  hung  outside  the 
window  with  its  bulb  at  the  same  level  as  that  of  the  thermometer 
inside.  It  has  been  found  by  experiment  that  when  the  thermometer 
on  the  outside  registers  exactly  the  temperature  of  that  on  the  inside 
the  interchange  of  heat  through  the  glass  is  negligible. 

One  of  the  duties  of  the  observer  at  the  table  is  to  record  the  temper- 
ature of  these  thermometers  frequently  and  make  such  alteration  in  the 
heating  or  cooling  of  the  laboratory  as  to  control  the  temperature 
within  the  necessary  limits.  Unfortunately  the  arrangement  of  the  heat- 
ing system  in  the  building  in  which  the  calorimeter  is  located  is  such 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT  OP  HEAT.       121 

as  to  necessitate  the  placing  of  the  steam-pipes  near  the  ceiling  of  the 
calorimeter  laboratory,  and  consequently  the  upper  layer  of  air  is  very 
much  warmer  than  that  near  the  bottom.  In  fact,  a  temperature  dif- 
ference of  from  6°  to  10°  is  not  at  all  uncommon.  By  means  of  two 
rotating  ceiling  fans,  however,  it  is  possible  to  distribute  the  warm  air 
and  thus  equalize  the  temperature  in  the  laboratory  to  a  considerable 
degree,  the  blades  of  the  fan  being  so  adjusted  as  to  force  the  warm  air 
downward.  Cooling  the  air  is  effected  by  opening  windows  at  different 
parts  of  the  laboratory.  By  these  means  it  has  been  found  possible  to 
regulate  the  temperature  opposite  the  window  of  the  calorimeter  with 
considerable  accuracy. 

Another  mercury  thermometer  is  hung  on  the  outside  of  the  rear  of 
the  calorimeter,  near  the  food  aperture.  This  likewise  serves  as  a  guide 
whereby  the  temperature  of  the  air  in  which  it  is  hung  may  be  kept  not 
far  from  20°,  i.  e.,  that  of  the  calorimeter  chamber.  Any  great  inter- 
change of  heat  through  the  food  aperture  is  thus  prevented.  Further- 
more, the  tube  of  the  food  aperture  is  surrounded  for  part  of  its  length 
by  the  air  in  the  inner  air-space  and  through  another  part  of  its  length 
by  the  air  in  the  outer  air-space,  and  the  temperature  of  these  portions  of 
the  tube  is  of  course  that  of  the  air  in  the  spaces,  which  is  controlled,  as 
explained  above,  in  accordance  with  that  of  the  chamber.  Interchange 
of  heat  between  the  metal  of  the  tube  and  the  orifice  in  the  metal  walls 
through  which  it  passes  is  prevented  by  the  rubber  tube  filled  with 
compressed  air  (D,  in  fig.  8)  by  which  they  are  separated. 

The  window  opening  in  front  of  the  calorimeter,  and  through  it  the 
food  aperture  in  the  rear  end,  may  be  plainly  seen  in  figure  30.  Adja- 
cent to  the  window  in  the  front  end  are  three  other  openings,  at  the 
places  where  the  dark  objects  are  seen  projecting  from  the  metal  wall. 
These  are  shown  in  detail  in  the  perspective  view  in  figure  33. 

The  smallest  of  these  openings,  near  the  lower  corner  of  the  window, 
is  for  the  passage  of  an  iron  rod,  which  is  the  axis  of  the  device  for 
raising  and  lowering  the  shields  to  the  heat-absorbers,  described  beyond. 
The  rod  is  fitted  very  closely  into  a  sleeve  in  the  copper  wall  through 
which  it  passes.  The  metal  of  the  rod  is  of  course  a  good  conductor 
of  heat,  but,  as  it  passes  through  the  two  outer  air-spaces,  its  temper- 
ature is  controlled  by  that  of  the  air  surrounding  it,  and  thus  little 
opportunity  is  afforded  for  the  passage  of  heat  through  it. 

The  larger  circular  opening  to  the  right  of  the  rod  (fig.  32)  is  very 
tightly  closed  by  a  wooden  plug  through  which  pass  the  two  pipes  for 
conducting  the  water  used  to  bring  away  heat  from  the  interior  of  the 
chamber,  as  explained  later.  The  wood  itself  is  a  very  poor  heat-con- 
ductor, and  furthermore  it  is  surrounded  by  the  two  air-spaces  in  which 


122  A    RESPIRATION    CALORIMETER. 

the  temperature  is  controlled  ;  hence  heat  is  not  conducted  from  the 
chamber  by  the  plug.  To  prevent  the  conduction  of  heat  through  the 
metal  pipes,  each  pipe  is  broken  about  half  way  through  the  plug  and 
the  ends  are  connected  by  rubber  tubing  (N,  fig.  32). 

The  other  opening,  which  is  rectangular  in  shape,  is  very  tightly 
filled  by  a  wooden  box  packed  with  plaster  of  Paris,  through  which 
pass  the  pipes  for  the  ingoing  and  the  outcoming  air.  Gain  or  loss  of 
heat  through  the  box  is  prevented  by  the  poor  conductivity  of  the  box 
and  packing  and  by  the  regulation  of  the  temperature  of  the  air  sur- 
rounding the  box.  To  prevent  loss  by  conduction  through  the  metal 
pipes,  each  pipe  is  broken  within  the  box  and  the  ends  connected  with 
rubber  tubing.  (See  H,  fig.  32.) 

The  nature  of  the  opening  in  the  side  for  the  electric  cable  tube  and 
that  in  the  top  for  the  weighing  apparatus  is  such  that  no  opportunity 
for  loss  of  heat  is  afforded. 

GAIN  OR  Loss  OF  HEAT  THROUGH  THE  AIR  CURRENT. 

As  explained  elsewhere,  part  of  the  heat  generated  within  the  cham- 
ber is  carried  out  as  latent  heat  of  water  vapor  in  the  outgoing  air.  So 
far  as  the  air  itself  is  concerned,  however,  gain  or  loss  of  heat  to  the 
chamber  due  to  cooling  or  heating  of  the  air  is  prevented  by  regulating 
the  temperature  of  the  air  entering  the  chamber  so  that  it  is  exactly 
the  same  as  that  leaving  it. 

The  difference  between  the  temperature  of  the  incoming  and  that 
of  the  outgoing  air  is  detected  by  means  of  iron  and  German-silver 
thermal  junctions,  of  much  simpler  construction  than  those  described 
above.  These  are  made  of  double  cotton-covered  insulated  wire,  and 
are  bound  tightly  together  in  the  center  like  a  sheaf  of  wheat,  the  bared 
ends  of  the  junctions  being  spread  out  and  separated,  thus  relying  on 
air  insulation.  These  junctions  are  installed  in  such  a  manner  that 
one  end  is  in  the  incoming  and  the  other  in  the  outgoing  air.  The 
apparatus  in  which  they  are  inserted,  designated  the  vestibule,  is 
shown  at  T.  in  figure  33.  It  consists  of  a  7.5  cm.  copper  pipe,  with  a 
copper  partition.  The  ends  of  the  thermal  junctions  are  on  opposite 
sides  of  this  partition.  The  air  entering  the  chamber  passes  along  the 
under  side,  and  that  leaving  is  in  contact  with  the  upper  side  of  the  par- 
tition. The  ends  of  the  junctions  are  connected  with  a  galvanometer, 
the  deflections  of  which  indicate  differences  in  temperature  of  the  air 
on  either  side  of  the  partition. 

The  incoming  air  is  heated  or  cooled  as  necessary,  in  order  that  the 
deflection  may  be  zero.  The  arrangements  for  heating  or  cooling  the 
air  are  shown  in  figure  32. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT   OF   HEAT.       123 

The  ingoing  air  is  caused  to  pass  over  a  32-candlepower  22o-volt 
lamp,  which  is  placed  in  an  enlargement  of  the  air-pipe  made  of  a  gal- 
vanized-iron  T  and  a  short  section  of  pipe,  with  a  cap.  The  position 
of  the  lamp  is  shown  in  figure  32.  The  connections  between  this  lamp 
and  the  electrical  circuits  are  shown  in  figure  37,  in  which  it  is  seen 
that  the  lamp-cord  is  connected  with  two  binding  posts  on  the  wall  of 
the  calorimeter.  These  binding  posts  are  connected  in  turn  by  two 
wires  leading  to  the  rheostat  on  the  observer's  table.  As  with  the 
heating  circuits  for  the  air-spaces  about  the  calorimeter,  here  also  the 
amount  of  heat  developed  in  the  electric  lamp,  and  consequently  the 
degree  of  warming  the  air  current,  can  be  regulated  with  great  exact- 
ness by  means  of  the  variable  resistance  (see  p.  1 18)  connected  with  the 
rheostat. 

When,  as  is  occasionally  the  case,  the  temperature  of  the  air  in  the 
calorimeter  laboratory  is  greater  than  that  of  the  interior  of  the  cham- 
ber, it  is  necessary  to  cool  the  air  current.  This  is  accomplished  by 
causing  a  current  of  cold  water  to  flow  through  a  lead  pipe  which  is 
closely  coiled  about  the  ingoing  air-pipe.  The  lead  pipe  is  connected 
at  one  end  with  the  water  supply  and  at  the  other  end  with  the  drain. 
By  opening  a  small  wheel  valve  at  the  extreme  left  of  the  lower  row  of 
valves  at  the  observer's  table  (see  fig.  37)  water  can  be  caused  to  pass 
through  this  pipe  and  effect  the  cooling  of  the  air.  To  prevent  sudden 
changes  caused  by  variations  in  the  room  temperature,  the  lead  pipe  is 
covered  with  cotton  felt  and  canvas,  as  is  seen  in  figures  3  and  37. 

MEASUREMENT   OF   HEAT. 

It  has  been  stated  that  most  of  the  heat  generated  within  the  chamber 
is  carried  away  by  a  current  of  cold  water.  The  quantity  thus  brought 
out  is  determined  from  the  amount  of  water,  its  rise  in  temperature, 
and  the  specific  heat  of  water  at  different  temperatures.  The  devices 
for  absorbing  the  heat  and  the  method  of  determining  the  quantity 
generated  are  here  described.  For  illustration  of  this  description  refer- 
ence is  continually  made  to  the  view  of  the  interior  of  the  chamber 
shown  in  figure  33. 

THE  HKAT-ABSORBING  SYSTEM. 

The  device  for  absorbing  heat  is  shown  at  H,  H,  H,  in  figure  33. 
Copper  pipe,  of  about  10  mm.  outside  diameter,  bent  to  conform  to 
the  shape  of  the  chamber,  is  suspended  from  the  ceiling  at  about  13 
cm.  from  each  wall.  A  large  number  of  sheet  copper  disks,  about 
5  cm.  in  diameter,  are  soldered  along  the  pipe  at  intervals  of  about  I 
cm.,  their  purpose  being  to  increase  the  area  of  surface  exposed  to 


I24 


A    RESPIRATION   CALORIMETER. 


the  heat.  Two  coils  of  such  pipe,  one  above  the  other,  comprise  the 
heat-absorber.  The  water  for  taking  away  the  heat  enters  the  calo- 
rimeter chamber  through  a  brass  tube  in  the  wooden  plug  in  the  front 
end  of  the  chamber,  flows  through  the  rubber  tube  Wj  into  the  lower 


Pro.  32.— Sectional  View  of  Walls  of  the  Chamber,  showing  method  of  installing  air-pipes,  water- 
pipes,  and  rod  for  raising  and  lowering  shields.  The  copper  wall  A,  zinc  wall  B,  and  two 
wooden  walls  C  and  D  are  penetrated  by  the  box  E  for  the  air-pipes  F  and  G  and  by  the  wooden 
plug  K.  The  electrical  lamp  I  shows  method  of  heating,  and  the  water  coil  J  that  of  cooling,  the 
ingoing  air. 


to  face  page  124. 


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THE   CALORIMETER  SYSTElt   AND   MEASUREMENT   OF   HEAT.      125 

pipe  of  the  heat- absorber,  passes  once  around  the  chamber,  then  enters 
the  upper  pipe  and  makes  another  circuit  of  the  chamber,  and  finally 
passes  out  of  the  chamber  by  way  of  the  wooden  plug  through  another 
brass  pipe  connected  by  the  rubber  tube  W2.  With  this  arrangement 
the  water  absorbs  heat  very  rapidly,  although  the  actual  mass  of  water 
inside  the  calorimeter  at  any  one  time  is  kept  at  a  minimum,  i.  <?.,  the 
contents  of  the  pipe  of  the  absorber,  about  400  grams. 

REGULATION  OP  RATE  OF  ABSORPTION   OF   HEAT. 

In  order  that  the  temperature  of  the  chamber  may  be  kept  constant, 
it  is  necessary  to  provide  that  the  rate  at  which  heat  is  absorbed  may 
be  varied  in  accordance  with  that  at  which  it  is  produced.  This  is  accom- 
plished in  different  ways.  The  coarser  regulations  are  easily  made  either 
by  increasing  the  flow  of  water  through  the  system  or  by  lowering  the 
temperature  of  the  ingoing  water.  The  finer  regulations  that  are  essen- 
tial for  maintaining  a  constant  balance  between  heat  production  and 
heat  absorption  are  made  by  increasing  or  diminishing  the  amount  of 
heat-absorbing  surface  exposed,  by  lowering  or  raising  shields  (Sd,  in 
ng-  33)  provided  for  the  purpose.  When  the  shields  are  raised  the  air 
in  them  is  cooled,  and,  serving  as  heat  insulation,  retards  the  absorp- 
tion. When  the  shields  are  lowered  the  absorbing  surface  is  exposed 
directly  to  the  heat. 

The  shields  are  constructed  of  sheet  aluminum.  The  shorter  ones, 
which  protect  the  absorbers  on  the  ends  of  the  chamber,  are  raised  or 
lowered  when  necessary  by  the  subject  inside  the  chamber.  Those  on 
the  sides  are  operated  by  the  observer  outside.  A  flexible  cord  attached 
to  each  of  these  side  shields  travels  over  pulleys  and  connects  with  an 
iron  quadrant  on  the  rod  which  extends  through  the  wall  of  the  appa- 
ratus and  transmits  the  motion  of  the  hand  lever,  shown  in  figure 
32.  It  is  thus  possible,  by  raising  or  lowering  this  lever,  to  raise  or 
lower  the  long  shields  inside  the  chamber,  and  the  distance  through 
which  these  shields  are  raised  or  lowered  determines  the  area  of  the 
absorbing  system,  either  exposed  or  covered  up.  A  graduated  arc  over 
which  the  hand  lever  travels  permits  of  very  slight  motions  in  the 
movement  of  the  lever,  and  consequently  of  the  most  delicate  adjustment 
of  the  position  of  the  shields. 

In  ordinary  experiments  the  two  end  shields  are  always  up,  and  all 
the  finer  regulation  is  done  by  means  of  the  two  long  shields.  During 
the  night,  and  when  the  subject  is  sound  asleep,  it  is  necessary  to  raise 
these  shields  to  the  highest  point,  cut  down  the  rate  of  flow  of  water 
to  a  minimum,  and  raise  the  temperature  of  the  incoming  water  until 
it  is  nearly  at  the  top  of  the  scale  on  the  incoming  water  thermometer. 
During  work  experiments  all  the  shields  are  lowered  as  far  as  they 


126  A   RESPIRATION   CALORIMETER. 

will  go,  the  incoming  water  is  cooled  to  as  near  zero  as  possible,  and 
the  rate  of  flow  through  the  absorbing  system  is  at  the  maximum. 
Indeed,  in  one  series  of  experiments  with  a  professional  athlete  a  third 
pipe  with  disks  was  suspended  above  the  absorber  system,  thus  increas- 
ing the  heat-absorbing  area  by  50  per  cent. 

It  is  thus  seen  that  the  heat-absorbing  capacity  of  this  form  of  ab- 
sorber can  be  varied  within  very  wide  limits.  It  is  possible  to  vary 
the  rate  of  heat  absorption  with  this  apparatus  so  as  to  bring  away  as 
low  as  40  calories  per  hour  and  as  high  as  600  calories  per  hour.  Both 
of  these  measurements  being  irrespective  of  the  amount  of  heat  required 
to  vaporize  the  water  vapor  issuing  in  the  air  current,  they  indicate  the 
heat-absorbing  capacity  of  this  form  of  absorber  rather  than  the  heat- 
measuring  capacity  of  the  calorimeter. 

Besides  serving  to  increase  and  diminish  the  effective  surface  of  the 
absorbing  system,  these  troughs  and  the  gutters  attached  to  them  serve 
also  the  important  purpose  of  collecting  the  large  quantity  of  water 
which  condenses  on  the  surface  of  the  absorbers  and  the  shields,  as 
explained  on  page  23. 

SUPPLY  OF  WATER  FOR  MEASURING  HEAT. 

A  regular  pressure  of  water  in  the  absorber  pipe  is  quite  essential. 
Owing  to  the  marked  fluctuations  in  the  city  water  pressure,  the  water 
flowing  through  the  heat-absorber  system  is  taken  from  a  tank  in  the 
second  story  of  the  building  10  meters  above  the  point  at  which  it 
enters  the  calorimeter.  A  constant-level  attachment  on  the  tank  gives 
a  steady  pressure  and  flow  of  water. 

WATER   COOLERS. 

The  temperature  of  the  water  entering  the  calorimeter  is  regulated 
according  to  the  amount  of  heat  to  be  brought  away,  and  may  vary 
from  i°  to  12°.  In  order  to  secure  such  variation,  provision  is  made 
for  directing  a  portion  of  the  water  through  two  coils  of  iron  pipe  in 
tanks  that  can  be  filled  with  crushed  ice.  These  tanks  are  placed  in  a 
small  unheated  room  adjoining  the  calorimeter  laboratory.  Two  valves 
near  the  calorimeter  provide  a  means  for  mixing  the  cooled  water  and 
the  water  direct  from  the  supply  tank  in  whatever  proportions  are  de- 
sired. A  system  of  pipes  and  valves  makes  it  possible  to  use  either 
one  or  both  cooling  tanks  at  will. 

WATER  METER. 

To  determine  the  quantity  of  heat  brought  out  of  the  chamber  it  is 
necessary  to  measure  accurately  the  quantity  of  water  that  flows 
through  the  absorber.  Formerly  the  measurement  of  water  was  made 


TO  face  page  126. 


FIG.  34. — The  Water  Meter.  The  large  cans  in  which  the  water  collects  are  here  shown, 
together  with  method  of  attachment  to  balance-arm  and  lead  counterpoises  just  behind 
them.  Above  the  cans  may  be  seen  the  dials  on  which  the  weight  is  indicated,  and 
below  them  the  device  for  shifting  from  one  can  to  the  other.  The  various  electrical 
connections  are  also  shown. 


THE   CALORIMETER   SYSTEM,  AND   MEASUREMENT  OP   HEAT.      127 

by  volume,  by  alternately  filling  and  emptying  two  copper  cans  grad- 
uated in  liters.  This  method  involved  a  not  inconsiderable  error,  i.  e. , 
neglect  of  the  variation  in  density  of  water  at  different  temperatures. 
For  a  more  accurate  determination  of  the  quantity  of  heat,  therefore,  it 
is  essential  to  measure  the  quantity  of  water  by  weight.  For  this  pur- 
pose the  water-meter  or  balance  shown  in  figure  34  was  devised. 

A  copper  can  holding  about  10,000  grams  of  water  is  suspended  on 
one  arm  of  an  equal  beam,  and  a  lead  counterpoise,  equal  in  weight  to 
the  weight  of  the  can  and  about  9,800  grams  of  water,  is  suspended 
from  the  other  end.  In  addition,  the  remaining  weight  of  water  is 
taken  by  a  spring  balance,  which  indicates  about  400  grams  for  a  com- 
plete revolution  of  the  pointer.  When  the  can  is  nearly  filled  with 
water  and  the  weight  of  the  counterpoise  has  been  overcome,  the  beam 
begins  to  settle.  As  it  settles,  a  flexible  cord  attached  to  one  arm  of 
the  beam  throws  the  weight  upon  the  spring  balance,  and  the  pointer  on 
the  dial  indicates  the  exact  amount  of  weight  taken  care  of  by  the 
spring.  The  dial  is  graduated  into  100  divisions,  and  the  differences 
between  divisions  can  be  read  easily  by  halves. 

To  make  the  meter  as  nearly  automatic  as  possible  and  not  to  inter- 
rupt the  flow  of  water  through  the  calorimeter,  two  cans  are  provided, 
as  is  shown  in  figures  34  and  35. 

The  cans  and  balances  are  mounted  side  by  side  on  a  stout  wooden 
frame.  In  the  front  view,  figure  35,  the  two  cans  with  their  respect- 
ive balances  are  shown.  In  the  side  view  one  can,  the  equal  beam,  and 
the  lead  counterpoise  are  shown.  The  equal  beams  were  specially  made 
by  the  E.  &  T.  Fairbanks  Company,  of  Saint  Johnsbury,  Vermont.  It 
was  found  by  preliminary  tests  that  with  a  load  of  nearly  20  kg.  on  each 
arm,  differences  of  one  gram  could  be  detected.  The  spring  balances 
were  made  by  the  John  Chatillon  Company,  of  New  York.  These  are 
also  quite  sensitive. 

In  experiments  with  man  the  amount  of  water  passing  through  the 
heat-absorber  varies  greatly  at  different  times  in  the  same  experiment, 
and  especially  with  experiments  of  different  nature.  When  the  sub- 
ject is  asleep  in  the  middle  of  the  night,  10  kg.  of  water  passing  through 
the  absorber  system  above  described  will  suffice  to  bring  away  the  heat 
as  fast  as  it  is  generated  for  over  an  hour,  and  at  times  the  rate  of  flow 
may  even  be  cut  down  to  10  kg.  in  2  or  2^4  hours.  This  is  the  slowest 
rate.  During  periods  when  the  subject  is  hard  at  work,  on  the  other 
hand,  the  rate  is  much  faster,  a  flow  of  10  kg.  in  7  minutes  being  some- 
times necessary.  In  devising  the  water-meter,  therefore,  the  problem 
was  to  provide  for  the  accurate  weighing  of  as  much  as  80  kg.  of  water 
in  an  hour.  Furthermore,  in  order  that  the  observer  may  be  relieved 


128 


A    RESPIRATION   CALORIMETER. 


as  much  as  possible  from  the  necessity  of  manipulating  and  readjusting 
the  apparatus  every  few  minutes,  it  should  be  as  nearly  automatic  as 
practicable.  The  means  of  providing  for  alternate  filling  and  emptying 
of  the  cans  automatically  is  illustrated  in  figure  35. 


FIG.  35.— The  Water-Meter.  Diagrammatic  sections  showing  front  and  side  views.  The  two 
upper  cans  A  and  B  deliver  the  water  into  the  lower  cans  C  and  D  by  the  movement  of  valves 
between  these  two  cans.  The  bulk  of  the  weight  is  taken  up  by  the  lead  counterpoise  at  right 
of  beam  E. 

Just  below  the  spring  dials  a  small  cup-shaped  attachment  (water- 
receiving  chamber),  with  curved  tubes  from  the  bottom  on  each  side 
and  a  partition  in  the  middle,  is  attached  to  the  framework.  The 
current  of  water  to  be  measured  enters  through  a  piece  of  brass  pipe, 


THE   CALORIMETER  SYSTEM  '\ND   MEASUREMENT   OF   HEAT.       129 

the  lower  end  of  which  is  in  this  cup-shaped  vessel.  By  swinging 
this  pipe  through  a  small  arc  the  current  of  water  is  deflected  to  either 
side  of  the  partition  in  the  receiving  cup  and  directed  through  the 
bent  tubes  into  either  can.  This  pipe  is  moved  to  one  side  or  the  other 
by  means  of  wire  projections,  W,  extending  below  the  arms  of  the 
balance-beams.  When  one  can  is  full  of  water  and  sinks,  the  falling 
end  of  the  beam  pushes  against  the  wire  and  moves  the  outlet  pipe  so 
that  the  water  current  is  deflected  to  the  opposite  side  of  the  receiving 
cup,  from  which  it  flows  into  the  empty  can. 

As  the  full  can  sinks,  a  valve  in  the  outlet  pipe  is  opened  and  the 
water  drains  into  a  smaller  can,  D,  below.  While  this  is  filling  there 
is  no  loss  in  weight,  but  as  soon  as  it  is  full  the  water  begins  to  flow 
away  through  a  siphon,  and  also  through  an  overflow  pipe.  As  is 
seen  from  the  construction  in  the  drawing,  the  small  can  is  provided 
with  two  openings,  one  of  which,  the  overflow  C,  is  made  by  soldering 
a  piece  of  pipe  into  the  bottom  of  the  small  can  in  such  a  manner  that  the 
upper  end  of  the  pipe  nearly  touches  the  top  of  the  can.  A  small  siphon 
attached  to  a  nut,  F,  screwed  into  the  bottom  of  the  can  is  the  second 
opening.  As  soon  as  the  small  can  is  filled  the  siphon  is  started.  As 
the  diameter  of  the  siphon  tube  is  very  much  less  than  that  of  the 
opening  through  the  valve,  the  lower  chamber  fills  up  to  the  level  of 
the  overflow  C,  and  water  soon  begins  to  flow  out  of  this  opening. 
As  soon  as  all  the  water  has  passed  out  of  the  upper  can,  the  overflow 
through  the  large  tube  ceases  and  the  lower  can  is  completely  emptied 
by  means  of  the  siphon.  The  end  of  the  short  arm  of  the  siphon  nearly 
touches  the  bottom  of  the  small  depression  in  the  cap  F,  into  which 
all  the  water  from  the  can  drains.  It  is  thus  seen  that  the  lower  cham- 
ber is  constructed  on  the  principle  of  the  Tantalus  cup.  It  has  been 
found  by  repeated  experiment  that  the  quantity  of  water  adhering  to 
the  walls  of  both  the  upper  and  the  lower  cans  is  remarkably  constant. 

The  valves  in  the  outlets  to  the  large  cans  are  opened  or  closed  au- 
tomatically, as  the  balance-arm  assumes  a  level  position.  The  valve 
on  each  can  has  a  long  lever,  the  end  of  which  is  between  the  upper 
and  lower  compartments  of  the  other  can,  and  is  moved  upward  or 
downward  with  the  motion  of  the  can.  This  construction  is  seen  in 
figure  35.  Thus,  as  one  of  the  cans  sinks,  the  effect  is  to  open  the  valve 
at  the  bottom  of  the  moving  can  and  to  close  the  valve  at  the  bottom 
of  the  stationary  can. 

In  figure  35  the  water  is  shown  as  entering  the  right-hand  can. 
The  valve  between  the  upper  and  lower  can  is  represented  as  being 
closed.  If,  now,  this  can  settles,  the  water  will  be  deflected  to  the 
other  side  of  the  receiving  chamber,  the  handle  of  the  valve,  which 

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A    RESPIRATION   CALORIMETER. 


almost  touches  the  projection  on  the  upper  side  of  the  lower  compart- 
ment on  the  other  can,  will  be  moved  upward,  and  at  the  same  time  a 
projection  attached  to  the  bottom  of  the  can  will  accomplish  the  closing 
of  the  valve  on  the  other  can. 

In  order  that  the  force  required  to  open  and  close  the  valves  may 
not  interrupt  the  descent  of  the  can  and  interfere  with  the  proper 
weighing  of  the  water,  an  arrangement  for  increasing  the  momentum 
of  the  full  can  is  provided.  This  device  is  illustrated  in  figure  36. 

The  rod  on  which  the  counterpoise  is  suspended  from  the  beam  is 
tipped  on  the  lower  end  with  a  small  bulb  which  opens  the  jaws  of  a 
spring  clutch,  a.  By  means  of  a  small  nut  with  a  right  and  left  hand 
thread  the  tension  of  the  spring  may  be  varied  at  will,  and  is  so 
adjusted  that  a  pull  of  about  200  grams  is  necessary  to  release  the  bulb. 


FIG.  36. — Clutch  to  regulate  tension  on  Water-Meter.    Two  curved  steel  springs  hold  a 
bulb  on  the  end  of  a  steel  rod  at  bottom  of  lead  counterpoise  of  the  water-meter. 

When  the  tension  of  the  clutch  has  been  overcome  the  bulb  is  released 
rather  suddenly,  and  as  it  passes  through  the  jaws  of  the  clutch,  these 
snap  together,  and  their  converging  ends,  rubbing  on  the  bulb,  give  a 
distinct  impetus  to  the  upward  movement  of  the  counterpoise,  thereby 
imparting  momentum  to  the  whole  system.  By  this  means  sufficient 
force  is  obtained  to  operate  the  valves  ;  indeed,  the  end  of  the  beam 
that  bears  the  cans  is  invariably  forced  to  a  position  below  the  level,  and 
the  pointer  on  the  spring  balance  travels  much  farther  than  the  true 
weight  would  warrant.  The  spring  in  the  balance,  however,  soon  im- 
parts a  movement  in  the  opposite  direction.  This  reverse  movement  of 
the  spring  aids  materially  in  the  use  of  the  balance,  for  by  its  means 
the  balance-beam  is  drawn  a  little  distance  away  from  the  wire  projection 
used  to  deflect  the  water  current,  and  the  ends  of  the  levers  on  the 
valves  are  slightly  removed  from  the  projections  on  the  cans,  and  thus 
the  whole  system  is  freely  suspended.  Inasmuch  as  about  20  seconds 
elapse  in  the  passage  of  the  water  from  the  upper  chamber  to  the  lower 


THE  CALORIMETER   SYSTEM   AND   MEASUREMENT  OP   HEAT.       131 

chamber  before  the  water  actually  runs  out  of  the  system,  ample  time 
is  given  to  record  the  exact  position  of  the  pointer  on  the  dial.  After 
this  position  is  recorded,  the  apparatus  requires  no  more  attention  until 
the  next  can  is  filled.  As  soon  as  about  400  grams  of  water  have  run 
out  of  the  system,  the  equipoise  settles  back  to  the  position  shown  in 
the  diagram,  the  bulb  projection  on  the  bottom  of  the  counterpoise 
resuming  its  position  between  the  jaws  of  the  spring. 

As  a  result  of  the  impetus  given  the  system  by  the  spring  clutch, 
and  that  in  the  opposite  direction  by  the  balance-spring,  the  momentum 
of  the  large  mass  of  metal  and  water  has  a  tendency  to  cause  the  sys- 
tem to  oscillate  for  several  seconds  before  finally  assuming  a  position  of 
equilibrium.  Preliminary  experiments  showed  that  this  motion  per- 
sisted a  considerable  time — longer,  indeed,  than  the  20  seconds  required 
for  the  water  to  flow  into  the  lower  can  and  begin  to  run  out  of  the 
system.  Consequently  some  method  was  necessary  to  check  this  oscil- 
lation and  have  the  system  attain  equilibrium  as  rapidly  as  possible. 
To  accomplish  this  end,  an  iron  armature  (£  in  fig.  35)  was  fastened  to 
one  of  the  connections  between  the  upper  and  lower  cans.  An  electro- 
magnet was  fastened  to  the  upright  wooden  frame  supporting  the  whole 
system  in  such  a  position  that  when  the  can  was  released  and  was 
vibrating  back  and  forth  the  iron  armature  would  rub  over  the  end  of 
the  electro-magnet.  By  having  a  feeble  current  passing  around  the 
magnet,  the  movement  of  the  can  could  be  very  readily  checked. 

It  was  found,  however,  practically  impossible  to  regulate  the  strength 
of  the  current  so  as  to  retard  the  vibration  and  yet  not  hold  the  armature 
against  the  end  of  the  magnet,  and  thereby  prevent  the  system  from 
swinging  freely  and  being  weighed  accurately.  A  circuit-breaker  was 
devised  and  attached  to  the  shaft  supplying  power  to  the  calorimeter 
room.  (See  fig.  i . )  By  this  simple  device  the  current  is  made  and  broken 
every  few  seconds — indeed,  at  approximately  such  times  as  would  rep- 
resent the  end  of  the  vibration.  The  effect,  therefore,  is  to  have  the 
armature  attracted  by  the  magnet  and  held  firmly  for  an  instant ;  the 
current  is  then  broken  and  the  system  begins  another  oscillation,  at  the 
end  of  which  the  current  again  holds  the  system  for  an  instant,  the 
effect  being  to  diminish  the  momentum  each  time  the  armature  is  in 
contact  with  the  magnet.  Finally,  by  the  observer's  raising  a  switch 
and  thus  completely  breaking  the  current  around  the  magnet,  the  can 
swings  freely  and  may  be  weighed  accurately.  By  means  of  the  two 
nuts  on  the  central  rod  of  the  magnet  the  distance  of  the  ends  of  the 
magnet  from  the  armature  when  the  system  is  in  equilibrium  can  be 
altered  at  will. 


132  A   RESPIRATION   CALORIMETER. 

The  end  of  the  soft  iron  core  of  the  magnet  is  surrounded  by  a  brass 
cap,  which  gives  a  rounded  surface  at  the  end  of  the  coil,  so  that  when 
the  armature  settles  into  position  it  will  easily  slide  along  the  end  of 
the  magnet  and  not  catch  at  any  point.  The  current  used  to  magnet- 
ize these  fields  is  taken  from  the  observer's  table  (see  p.  136),  and  has 
in  series  with  it  two  i6-candlepower  no-volt  lamps,  one  of  them  being 
the  galvanometer  lamp.  The  strength  of  current  through  the  two 
magnets  is  varied  by  means  of  the  resistance  coil  R  shown  in  figure  35. 

The  equipoise  beam  in  its  descent  touches  the  wire  W,  used  to  deflect 
the  water  current,  thereby  closing  an  electric  circuit  and  causing  an 
electric  signal-bell  to  ring  continuously  until  the  operator  lifts  a  switch 
on  the  observer's  table.  In  operating  the  meter,  then,  the  only  care 
required  on  the  part  of  the  observer  is  to  see  that  the  readings  of  the 
pointer  on  the  dial  are  accurately  recorded  each  time  the  bell  rings. 

Calibration  of  the  meter, — The  meter  was  calibrated  by  weighing  the 
total  amount  of  water  delivered  from  each  can,  noting  carefully  the 
position  of  the  pointers.  For  this  purpose  a  large  enameled-ware  pot 
with  a  hard-rubber  cover  was  accurately  weighed  on  the  large  balance 
(p.  56) .  A  specially  constructed  funnel  was  placed  under  the  overflow 
and  siphon  of  one  of  the  cans  and  the  neck  of  the  funnel  inserted  in  a 
hole  in  the  cover  of  the  previously  weighed  pot.  When  the  can  was 
released  the  water  was  delivered  into  the  weighed  pot  instead  of  into 
the  drain.  After  all  the  water  had  drained  out  of  the  can  and  funnel, 
the  pot,  plus  the  water,  was  weighed.  These  weights  were  usually 
made  to  the  tenth  of  a  gram.  A  curve  was  plotted  which  showed  the 
weights  of  water  delivered  by  the  meter  with  the  pointer  at  different 
positions,  and  consequently  it  is  now  only  necessary  for  the  observer  to 
record  the  position  of  the  pointer. 

Accuracy  of  the  meter. — The  extreme  accuracy  of  this  water-meter 
has  been  surprising,  for  while  the  amounts  as  indicated  by  the  readings 
on  the  dial  may  be  from  i  to  2  grams  either  side  of  the  true  amount 
delivered,  these  differences  tend  to  counterbalance  each  other,  and  it  is 
safe  to  state  that  in  a  series  of  observations  10  cans  full,  or  100  kg.  of 
water,  will  be  weighed  to  within  a  very  few  grams. 

To  facilitate  in  ascertaining  the  weights  of  water  remaining  in  the 
can  at  the  end  of  a  short  period  in  which  less  than  10  kg.  of  water 
were  flowing,  a  water-gage  graduated  in  liters  is  attached  to  the  front 
of  each  can.  It  is  thus  possible  for  the  observer  at  the  end  of  a  period 
to  note  the  quantity  of  water  in  the  can  to  within  a  tenth  of  a  liter. 
A  more  exact  estimate  of  this  amount  can  be  made  by  noting  the  time 
between  the  emptying  of  the  last  can  and  the  end  of  the  period. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT   OP   HEAT.       133 

Check  measurements  of  the  accuracy  of  the  meter. — From  time  to  time 
the  accuracy  of  the  meter  is  checked  by  direct  weighing.  By  means 
of  the  pot  and  funnel  mentioned  above,  this  check  is  very  readily  and 
rapidly  carried  out.  Usually,  one  weighing  of  the  water  delivered  from 
each  can  is  all  that  is  required.  With  the  weighing,  the  reading  of  the 
pointer  is  taken  and  the  weight  actually  observed,  then  directly  com- 
pared with  the  weight  as  indicated  by  the  curve.  The  meter  has  been  in 
use  for  two  years  and  has  given  excellent  satisfaction. 

THERMOMETERS  FOR  MEASURING  TEMPERATURE  o*  WATER. 

The  temperature  of  the  water  for  absorbing  heat  is  measured  as  it 
enters  and  as  it  leaves  the  chamber.  The  thermometers  used  for  these 
measurements  are  seen  in  the  small  closet  on  the  front  wall  of  the  cal- 
orimeter, at  the  left  of  the  observer's  table,  in  figure  37.  The  method  of 
installing  them  in  the  water-pipes  may  be  seen  in  figure  32. 

These  thermometers  are  of  special  form.  They  are  L-shaped,  with 
one  arm  52  cm.  long  and  the  other  36  cm.  long.  The  arm  with  the 
mercury  bulb  is  inserted  in  the  water-pipe,  extending  through  the 
wooden  plug  (N,  N,  in  fig.  32),  the  length  of  the  arm  being  such  that 
the  bulb  comes  directly  under  the  upright  pipe  that  conducts  the  water 
to  or  from  the  heat-absorber.  By  this  provision  the  temperature  that 
affects  the  mercury  in  the  bulb  is  that  of  the  water  just  as  it  enters  or 
just  as  it  leaves  the  chamber. 

The  graduations  on  the  other  arm  of  the  thermometer  begin  just  above 
the  betid  and  extend  to  near  the  end  of  the  arm.  The  thermometer 
used  to  determine  the  temperature  of  the  ingoing  water  is  graduated 
from  zero  to  12°  in  fiftieths  of  a  degree.  The  12  degrees  of  the  grad- 
uation cover  a  section  of  the  stem  420  mm.  long,  thus  allowing  0.70  mm. 
for  each  one-fiftieth  degree,  or  0.35  mm.  for  each  one-hundredth  degree. 
Readings  can  be  taken  accurately  without  the  use  of  a  lens  to  one- 
hundredth  of  a  degree.  The  thermometer  for  the  temperature  of  the 
outgoing  water  is  graduated  from  8°  to  21°.  As  the  temperature  of 
the  calorimeter  chamber,  especially  in  the  summer  time,  frequently  goes 
above  21°,  an  enlargement  of  the  capillary  is  made  at  the  top  of  the 
thermometer  to  permit  of  the  expansion  of  the  mercury  without  danger 
of  breaking  the  instrument. 

The  thermometers  have  been  very  carefully  calibrated  twice  each  year, 
and  although  the  zero  points  changed  slightly  at  first,  they  have  appar- 
ently now  become  fixed.  The  readings  of  the  two  thermometers  were 
compared  with  those  on  a  metastatic  thermometer  of  the  Beckmann  type, 
manufactured  by  Fuess  and  calibrated  by  the  Physikalisch-technische 
Reichsanstalt,  of  Charlottenburg,  Germany. 


134  A   RESPIRATION   CALORIMETER. 

It  was  found  with  both  thermometers  that  the  maximum  corrections 
occurred  near  the  beginning  of  the  graduation,  and  that  along  toward 
the  top  of  the  scale  the  correction  became  smaller.  This  would  be 
expected  from  the  increase  in  length  of  the  column  of  mercury  pressing 
on  the  thermometer  bulb.  The  thermometer  readings  are  corrected 
accordingly,  and  only  the  corrected  readings  used  in  determining  the 
differences  in  temperatures. 

CORRECTION  FOR  PRESSURE  OF  WATER  ON  THE  MERCURY  BULB. 

As  pointed  out  by  Armsby,1  the  pressure  of  the  water  current  on  the 
bulb  of  the  thermometer  may  introduce  an  appreciable  error  in  measure- 
ment. Since  differences  in  temperature  are  what  is  desired,  this  error 
would  of  course  be  negligible  were  the  pressure  the  same  on  both 
thermometers.  This,  however,  is  not  the  case.  The  pressure  on  the 
thermometer  bulb  in  the  water  entering  the  chamber  is  greater  than  that 
on  the  bulb  of  the  second  thermometer,  as  the  latter  is  much  nearer  the 
water  exit.  It  was  found  by  actual  trial  that  when  the  water  was  pass- 
ing through  the  system  at  the  rate  of  10  kg.  in  7  minutes,  which  is  the 
maximum  rate  in  experiments,  suddenly  shutting  off  the  current  caused 
a  fall  of  0.07°  in  the  column  of  mercury  in  the  thermometer  in  the 
ingoing  water,  and  of  0.015°  in  that  of  the  thermometer  in  the  outgoing 
water.  For  this  rate  of  flow,  therefore,  the  mercury  in  the  ingoing  water 
thermometer  reads  0.07°  too  high,  and  that  of  the  outgoing  water  ther- 
mometer 0.015°  to°  high.  Unless  these  corrections  are  applied,  the 
difference  in  temperature  is  obviously  0.055°  too  low;  consequently  this 
amount  is  added  to  the  difference  as  observed.  The  necessary  correc- 
tions for  all  rates  of  flow  occurring  in  actual  experiments  have  been 
determined  and  are  always  applied  to  the  readings,  though  in  many  of 
the  experiments  the  rate  of  flow  is  so  slow  that  the  effect  of  pressure 
on  the  bulb  is  inappreciable. 

MEASUREMENT  OF  TEMPERATURE  OF  THE  CALORIMETER. 

It  has  been  stated  that  the  rate  at  which  heat  is  absorbed  and  carried 
out  of  the  chamber  is  regulated  in  accordance  with  that  at  which  it  is 
generated  within  it,  so  that  the  temperature  of  the  chamber  may  be 
kept  constant.  To  this  end  it  is  necessary  to  be  able  to  determine 
fluctuations  in  the  temperature  of  the  chamber. 

While  mercury  thermometers  have  been  used  to  indicate  the  temper- 
ature of  the  water  current  in  the  heat-absorbing  system,  their  use  in 
measuring  the  temperature  of  the  air  in  the  calorimeter,  or  of  the  metal 
walls  of  the  chamber,  has  not  been  successful,  and  we  rely  on  the 
measurement  of  changes  in  resistance  of  coils  of  pure  copper  wire  which 
are  distributed  at  several  points  on  the  walls  of  the  chamber. 

1U.  S.  Dept.  of  Agr.,  Bureau  of  Animal  Industry  Bull.  51,  p.  34. 


THE;  CALORIMETER  SYSTEM  AND  MEASUREMENT  OF  HEAT.     135 

The  resistance  of  pure  copper  wire  to  the  passage  of  an  electric  cur- 
rent increases  proportionally  with  the  temperature.  By  means  of  a 
Wheatstone  bridge  and  a  delicate  galvanometer  it  is  possible  to  meas- 
ure with  great  accuracy  the  changes  in  resistance  of  a  coil  due  to  tem- 
perature fluctuations.  Where,  as  in  this  case,  temperature  differences 
rather  than  absolute  temperatures  are  involved,  the  problem  becomes  a 
comparatively  simple  one. 

Inasmuch  as  the  average  temperature  of  the  whole  mass  of  air  inside 
the  chamber  is  desired,  it  is  necessary  to  distribute  the  coils  in  such 
manner  that  the  variations  in  resistance  will  represent  as  closely  as 
possible  the  actual  temperature  fluctuations  of  the  air.  For  this  pur- 
pose the  amount  of  wire  the  resistance  of  which  is  to  be  measured  is 
wound  on  five  separate  coils  connected  in  series  and  suspended  from 
hooks  at  different  points  on  the  walls  of  the  chamber.  Whatever  local 
temperature  fluctuations  there  may  be  in  the  different  parts  of  the 
chamber,  each  coil  will  rapidly  acquire  the  temperature  of  the  air  im- 
mediately surrounding  it,  and  consequently  the  average  variations  of 
the  five  coils  taken  as  a  whole  will  closely  approximate  the  average 
temperature  fluctuations  of  the  air  inside  the  chamber. 

The  coils  consist  of  No.  32  pure  copper  wire,  double-silk  covered. 
They  are  wound  on  wooden  frames  and  are  well  protected  by  metal 
guards.  The  total  resistance  of  the  coils  is  not  far  from  20  ohms. 
Variations  in  resistance  which  indicate  temperature  changes  of  0.01° 
are  easily  detected  by  the  Wheatstone  bridge  and  galvanometer  used  in 
connection  with  these  coils. 

These  coils  (T,,  fig.  33),  suspended  as  they  are  about  2.5  cm.  from 
the  copper  wall,  acquire  the  temperature  of  the  air  rather  than  that  of 
the  copper  wall  itself.  In  determining  accurately  the  temperature 
changes  of  the  whole  mass  of  material,  it  is  frequently  desirable  to 
know  the  temperature  changes,  not  only  of  the  air,  but  of  the  copper 
wall.  For  this  purpose  four  copper  coils  (Tw,  fig.  33) ,  having  an  aggre- 
gate resistance  of  about  20  ohms,  are  wound  on  wooden  frames  and 
slipped  into  copper  pockets  made  by  soldering  a  copper  box  to  the  copper 
wall.  These  coils,  therefore,  are  likely  to  assume  the  temperature  of  the 
copper  wall  rather  than  that  of  the  air.  The  temperature  changes  can 
be  detected  by  means  of  the  switch,  galvanometer,  and  bridge  as  closely 
as  suggested  above  for  differences  in  temperature  of  the  air. 

Variations  in  resistance  of  the  copper  coils  are  detected  by  means  of 
a  Wheatstone  bridge  and  a  galvanometer.  For  many  years  we  have 
used  a  D' Arsonval  galvanometer  constructed  by  O.  S.  Blakeslee  in  the 
mechanical  laboratory  of  Wesleyan  University.  This  instrument  is 
very  sensitive  and  dead  beat,  allowing  10  readings  each  minute.  The 


136  A    RESPIRATION   CALORIMETER. 

phosphor-bronze  suspension  wire  of  the  instrument  is  still  intact  after 
eight  years'  use. 

The  galvanometer  is  placed  in  a  black-cloth  hood,  shown  in  figure 
37,  and  a  straight  filament,  i6-candlepowerlamp  (a  so-called  bung- hole 
lamp)  used  as  a  source  of  illumination,  the  image  of  the  filament  being 
reflected  on  a  millimeter  scale  immediately  before  the  observer. 

The  variations  in  resistance  of  the  copper  coils  can  be  measured  in 
two  distinct  ways.  In  the  one  case  it  is  possible  to  adjust  a  very  deli- 
cate variable  resistance  so  that  by  comparing  the  resistances  of  the 
copper  coils  with  a  Wheatstone  bridge  the  slight  variations  in  resist- 
ance due  to  temperature  fluctuations  can  be  expressed  in  fractions  of 
an  ohm.  The  second  method  depends  upon  the  fact  that  the  deflec- 
tions on  the  galvanometer  are  very  nearly  proportional  to  the  amount 
of  current  passing  through  it,  and  consequently  slight  variations  in  the 
current  caused  by  slight  alterations  in  resistance  will  produce  corre- 
sponding alterations  in  the  deflection  of  the  galvanometer.  The  amount 
of  current  passing  through  the  galvanometer  is  a  function  of  two  vari- 
ables—  electro  motive  force  and  resistance.  If  the  electro-motive  force 
is  maintained  constant,  any  alterations  in  resistance  of  the  copper  ther- 
mometer coils,  through  which  the  current  must  flow  when  passing 
through  the  galvanometer,  will  result  in  variations  in  the  amplitude  of 
the  galvanometer  deflection. 

The  first  method  of  temperature  measurements,  i.  e.,  the  use  of  the 
slide- wire  Wheatstone  bridge,  was  followed  entirely  in  the  earlier  form  of 
respiration  calorimeter,1  but  the  long-continued  use  of  the  slide-wire 
bridge  is  open  to  serious  objections.  Temperature  measurements  in 
experiments  with  the  respiration  calorimeter  are  made  at  intervals  of 
not  more  than  4  minutes,  and  frequently  the  experiments  continue  from 
10  to  13  days.  The  constant  wear  and  tear  of  the  sliding  contact  on  a 
bridge  of  this  type  is  a  factor  that  must  be  taken  into  account  in  the 
most  accurate  work,  and  accordingly  we  have  devised  an  apparatus  for 
indicating  temperature  changes  on  the  second  of  the  two  plans  outlined 
above.  This  apparatus  is  described  in  detail  on  pages  139-150. 

OBSERVER'S  TABLE. 

The  various  devices  concerned  in  the  regulation  of  the  temperature 
of  the  calorimeter  and  the  measurement  of  heat  are  controlled  from  the 
observer's  table  at  the  front  of  the  apparatus.  Figure  37  gives  a  gen- 
eral view  of  the  table  and  the  adjacent  apparatus. 

The  wires  from  the  systems  of  thermal  junctions  in  the  metal  walls  and 
the  surrounding  air-spaces,  and  those  from  the  resistance  thermometers 

*U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63,  pp.  25-27. 


To  face  page'  136, 


FIG.  37.— Observer's  Table.  At  left,  the  window,  lever  for  raising  shields,  and  water  ther- 
mometers ;  on  table  at  left  is  the  rheostat,  above  it  the  valves  for  controlling  cooling 
water,  and  in  the  center  of  table  the  mercury  switch.  Incidental  electrical  connec- 
tions and  instruments  are  shown  on  right  of  table.  The  galvanometer  scale  is  imme- 
diately above  table. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT  OP   HEAT.       137 

within  the  chamber,  pass  out  through  a  groove  in  the  under  side  of  the 
circular  wooden  plug  projecting  from  the  wooden  walls  at  the  left  of 
the  table  and  terminate  in  the  mercury  switch  at  the  rear  of  the  center 
of  the  table.  This  switch  is  described  in  detail  beyond. 

The  electrical  connections  for  the  heating  systems  in  the  different 
sections  of  the  air-spaces  are  made  through  the  rheostat  at  the  rear 
of  the  left  end  of  the  observer's  table.  Inasmuch  as  there  are  eight 
sections  of  the  air-spaces,  and  one  resistance  lamp  is  used  to  vary  the 
temperature  of  the  incoming  air,  the  rheostat  has  nine  sections,  each  of 
which  is  connected,  by  means  of  a  cable  passing  through  the  floor  of  the 
platform  (seen  under  the  table  in  fig.  37),  with  its  resistance  coil  lying 
between  the  respiration  chamber  and  the  floor,  as  explained  on  page  1 18. 

The  flow  of  water  through  the  pipes  for  cooling  the  different  sections 
of  the  air-spaces,  and  through  the  pipe  for  cooling  the  ingoing  air,  is 
regulated  by  the  ten  valves  immediately  above  the  rheostat.  The  upper 
four  valves  control  the  four  sections  of  the  inner  air-space,  the  four 
immediately  beneath  them  those  of  the  outer  air-space,  and  the  fifth 
valve  on  the  lower  line,  the  circuit  for  coolingthe  ingoing  air.  The  valve 
at  the  extreme  left  is  used  to  maintain  a  constant  flow  of  water  into  the 
supply  tank  in  another  part  of  the  building.  (See  p.  126.)  At  the  right 
of  the  table*  are  several  resistance  coils,  and  upon  the  table  a  portable 
voltmeter,  used  in  electrical  check  experiments.  (See  p.  169.) 

The  millimeter  scale  on  which  the  deflections  of  the  galvanometer  are 
read  is  immediately  in  front  of  a  small  clock  on  the  black-cloth  hood 
in  which  the  galvanometer  is  placed.  The  two  upright  thermometers 
inserted  in  the  wooden  plug  at  the  left  of  the  observer's  table  indicate 
the  temperatures  of  the  ingoing  and  outcoming  water  for  the  heat- 
absorbing  system.  A  little  below  and  at  one  side  is  seen  the  lever  for 
raising  or  lowering  the  shields  to  the  heat-absorbers  inside  the  chamber. 
This  moves  over  a  graduated  arc  into  which  a  peg  on  the  handle  fits, 
thus  allowing  for  fine  adjustments.  Of  the  three  small  switches  under 
the  edge  of  the  table,  at  the  left,  one  completes  the  telephone  circuit 
to  the  chamber  and  the  others  are  for  connections  with  the  bicycle 
ergometer  (see  p.  164)  and  with  electrical  devices  used  within  the  cham- 
ber in  electrical  check  experiments. 

The  water-meter,  which  is  not  shown  in  figure  37,  stands  on  the  floor 
immediately  at  the  right  of  the  observer,  as  it  appears  in  figure  3. 
Thus  it  is  seen  that  from  the  position  of  his  chair  the  observer  can  note 
through  the  glass  door  the  movements  of  the  subject  inside  the  chamber, 
read  the  mercurial  thermometers  in  the  water-cooling  circuit,  heat  or 
cool  various  sections  of  the  chamber,  raise  or  lower  the  shields,  note 
temperature  differences  on  the  galvanometer,  and  note  the  quantity  of 
water  passing  through  the  water-meter. 


138 


A   RESPIRATION   CALORIMETER. 


ELECTRICAL  CONNECTIONS  ON  THE  TABLE. 

The  scheme  of  the  various  electrical  connections  on  the  observer's 
table  is  given  in  figure  38. 

*2    "I        *3 


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STORAGE       BATTERY 


FIG.  38. — Electrical  Connections  on  the  Observer's  Table.  All  electrical  connections  are,  for  con- 
venience, brought  to  the  observer's  table.  The  rheostat  controlling  the  heating  circuits,  the 
mercury  switch,  the  thermal  junctions  and  thermometer  circuits,  and,  at  right,  connections 
for  storage  battery  for  use  in  electrical  check  experiments  and  for  magnetizing  the  fields  of 
the  bicycle  ergometer  are  shown. 


THE   CALORIMETER  SYSTEJH   AND   MEASUREMENT   OF   HEAT.       139 

The  thermal  junctions  are  indicated  in  the  upper  left-hand  corner  by 
the  numbers  1,2,  and  3.  In  No.  i  there  are  four  subdivisions  corre- 
sponding to  the  four  sections — top,  upper  zone,  lower  zone,  and  bottom — 
of  the  metal  walls  of  the  chamber.  No.  2,  which  is  here  indicated  as 
in  series  with  No.  i,  represents  the  thermal  junctions  in  the  air  cur- 
rent. No.  3  represents  the  four  subdivisions  of  the  system  of  thermal 
junctions  in  the  inner  and  outer  air-spaces. 

The  resistance  thermometers  for  indicating  temperature  changes  in 
the  air  of  the  chamber  and  the  copper  wall  are  represented  by  the  coils 
5,  7,  and  R.  These  are  here  shown  to  be  connected  so  as  to  have  one 
common  return.  The  coil  W  represents  a  resistance  thermometer  for 
measuring  differences  in  temperature  of  ingoing  and  outgoing  water 
for  heat  absorption.  (See  p.  149.) 

All  the  above  connections  terminate  in  the  mercury  switch  at  the 
rear  of  the  center  of  the  table.  Extending  backward  from  this  are 
two  wires  leading  to  the  galvanometer. 

In  the  upper  right-hand  corner  of  the  table  is  the  rheostat  controlling 
the  heating  circuits.  No.  i  represents  the  four  circuits  in  the  different 
sections  of  the  inner  air-space  and  No.  3  the  circuits  for  the  corre- 
sponding sections  of  the  outer  air-space.  The  32-candlepower  lamp  is 
that  used  in  heating  the  ingoing  air.  The  switch  in  the  upper  right- 
hand  corner  of  the  diagram  connects  the  rheostat  with  the  city  electric 
main. 

On  the  lower  right-hand  corner  are  wires  leading  to  a  storage  bat- 
tery. The  binding  posts  numbered  3,  4,  5,  and  6  are  for  connections 
for  electric  check  tests  and  for  magnetization  of  the  fields  of  the  bicy- 
cle ergometer. 

MERCURY  SWITCH   AND  BRIDGE. 

In  order  to  keep  the  two  metal  walls  of  the  chamber  adiabatic,  each 
thermal  junction  system — i.  <?.,  those  corresponding  to  the  top,  upper 
zone,  lower  zone,  and  bottom — is  connected  so  that  the  differences  in 
electro- motive  forces  of  the  junctions  in  thermal  contact  with  the  zinc 
and  the  copper  walls  can  be  measured  on  the  galvanometer  and  thus 
furnish  an  indication  as  to  whether  the  zinc  wall  should  be  warmed  or 
cooled.  Similarly,  the  four  outer  thermal  junction  systems  in  the  inner 
wooden  wall  are  so  connected  that  they  may  be  put  in  series  with  the 
galvanometer.  Not  only  are  the  individual  sections  of  these  two  ther- 
mal junction  systems  thus  connected,  but  the  wiring  is  such  that  the 
algebraic  sum  of  the  electro-motive  forces  of  the  junctions  in  all  four 
sections  may  be  noted  for  each  system  ;  consequently  there  are  five 
connections  necessary  for  each  system,  i.  e.,  the  four  parts  and  the 


140 


A    RESPIRATION   CALORIMETER. 


whole.  The  thermal  junction  system  in  the  air  current  is  likewise 
capable  of  being  placed  in  series  with  the  galvanometer.  There  are, 
then,  eleven  different  thermal  junction  connections  to  be  made  with  the 
galvanometer. 

Any  system  of  switches  for  such  a  number  of  connections  must  obvi- 
ously be  somewhat  complex,  and,  furthermore,  the  wear  and  tear  on 
them  would  be  such  as  to  render  their  use  extremely  unsatisfactory. 
The  sliding  contacts  would  frequently  become  covered  with  dirt  or  grit, 


IfiQ.  39.— Unit  Key  of  Mercury  Switch.  By  depressing  the  key  the  two  ends  of  a  copper  link  are 
caused  to  dip  into  mercury  in  holes  in  a  wooden  block.  The  mercury  insures  connection  of  the 
screw  and  nut  with  the  proper  electrical  devices. 

and  the  working  parts  would  soon  give  way.  An  ingenious  method  of 
using  mercury  contacts  for  the  thermal  junction  systems,  thereby  avoid- 
ing poor  contacts  and  excessive  wear  and  tear,  was  devised  by  our 
mechanician,  Mr.  S.  C.  Dinsmore.  Later,  this  mercury  contact  device 
was  incorporated  in  an  instrument  which  combined  a  mercury  switch 
and  a  bridge  system. 

The  connection  between  each  thermal  junction  circuit  and  the  galva- 
nometer is  made  by  dipping  two  copper  links  into  four  mercury  cups, 
two  of  which  are  connected  with  the  wires  leading  from  the  thermal 


to  face  page  140. 


Fio.  40.— Meicury  Switch,  top  removed.  At  left,  the  switch  with  its  mercury  cups  and  comparison 
coils ;  at  right,  the  top  with  the  keys  and  copper  links.  In  the  foreground  are  shown  the  com- 
parison coils  and  nuts  for  holding  top  in  place. 


FIG.  4t. — General  View_of  Mercury  Switch. 


Fio.  42. — Under  side  of  Mercury  Switch,  showing  electrical  connections. 


THE   CALORIMETER   SYSTE^I   AND   MEASUREMENT   OF   HEAT.       141 

junction  system  and  two  with  wires  extending  to  the  galvanometer. 
The  special  feature  of  this  switch  is  the  device  for  closing  the  circuit. 
The  two  copper  links,  each  of  which  is  in  fact  composed  of  several 
strands  of  No.  16  copper  wire,  are  fastened  to  a  square  of  hard  rubber 
on  the  end  of  a  steel  rod.  A  cross-section  of  a  unit  connection  on  this 
switch  is  shown  in  figure  39. 

A  hole  drilled  in  a  block  of  oak  serves  as  the  mercury  cup.  At  the 
bottom  of  each  cup  there  is  an  iron  or  steel  screw  which  extends  through 
the  oaken  block  to  a  brass  nut  on  the  under  side.  The  wires  leading 
to  the  galvanometer  and  thermal  junction  circuit,  respectively,  are  sol- 
dered to  the  brass  nuts.  The  holes  in  the  oaken  block  used  for  mercury 
cups  are  shown  at  the  left  in  figure  40.  The  wood  was  boiled  for  sev- 
eral hours  in  paraffin  and  a  thick  coating  of  paraffin  covers  all  of  it. 
The  crater-like  appearance  of  each  hole  is  due  to  the  deposit  of  par- 
affin about  the  rim. 

The  cover  of  the  switch,  which  is  not  so  thick  as  the  base,  is  made 
of  mahogany.  The  steel  rod  to  which  the  square  of  hard  rubber  with 
the  copper  links  is  attached  passes  through  a  metal  bushing  set  in  the 
cover,  and  the  two  copper  links  are  held  suspended  over  the  mercury 
cups  by  a  spring  coiled  around  the  steel  shaft.  On  the  upper  end  of 
the  steel  shaft  a  hard-rubber  button  is  attached.  A  steel  guide  wire 
driven  into  the  cover  and  passing  through  a  hole  in  the  square  of  hard 
rubber  insures  the  copper  links  entering  the  mercury  cups  in  the  proper 
position  when  the  key  is  pressed.  The  manipulation  is  not  unlike  that 
of  depressing  the  key  of  a  typewriter,  save  that  the  key  is  held  down 
for  several  seconds.  The  details  of  the  under  side  of  the  cover  are 
shown  in  the  right-hand  portion  of  figure  40. 

The  whole  switch,  with  the  cover  in  place,  is  shown  in  figure  41 .  In 
figure  37  the  switch  may  be  seen  in  position  on  the  observer's  table. 
Some  idea  of  the  intricacy  of  the  wiring  is  obtained  from  the  view  given 
in  figure  42,  which  shows  the  under  side  of  the  switch. 

The  details  of  the  electrical  connections  between  the  switch  and  the 
different  parts  of  the  calorimeter  with  which  it  is  concerned  are  illus- 
trated in  figure  43. 

Here  it  is  seen  that  a  number  of  connections  other  than  those  having 
to  do  with  the  thermal  junction  system  are  included  in  this  switch.  To 
distinguish  the  different  thermal  junction  systems,  we  have  designated 
those  belonging  to  the  system  between  the  two  metal  walls  of  the  cham- 
ber as  No.  i  ;  those  in  the  air  current  as  No.  2,  and  those  in  the  inner 
wooden  walls  as  No.  3.  The  different  sections  of  circuits  Nos.  i  and 
3  are  further  subdivided  into  top  (T),  upper  zone  (U),  lower  zone  (I,), 
and  bottom  (B).  Consequently  the  circle  on  figure  43,  in  which  the 


142 


A    RESPIRATION   CALORIMETER. 


designation  T  No.  3  is  placed,  represents  the  outline  of  the  key,  which, 
when  pressed,  will  connect  the  two  wires  leading  from  the  upper  section 
of  the  thermal  junction  system  in  the  inner  wooden  wall  with  the  two 
wires  leading  to  the  galvanometer. 


BATTER*        ADJ.  RES. 


WATER 

LEAVING 


Kio.  43. — Diagram  of  Electrical  Connections  of  Mercury  Switch.  The  upper  portion  of  diagram 
represents  the  thermometers  and  junctions  and  the  galvanometer  with  which  the  bridge  is 
connected. 

The  four  sections  of  this  thermal  junction  system  are  connected  with 
the  four  upper  keys  of  the  switch.  The  four  sections  of  the  inner 
thermal  junction  system,  z*.  <?.,  No.  i,  are  connected  with  the  four  keys 
immediately  beneath  those  for  system  No.  3.  In  order  that  the  alge- 
braic sum  of  the  electro-motive  forces  for  the  four  parts  of  system 


THB   CALORIMETER   SYSTEM   AND   MEASUREMENT   OF   HEAT.       143 

No.  i  may  be  read  at  once,  the  outer  connecting  wires  which  take  in  all 
the  junctions  in  system  No.  i  are  carried  to  the  mercury  cups  beneath 
the  key  designated  A  L,  L,  No.  i .  As  is  seen  on  page  1 16,  this  deflection 
corresponds  to  the  average  temperature  difference  between  the  zinc  and 
copper  wall.  In  the  same  way  the  algebraic  sum  of  the  deflections  of 
the  four  parts  of  No.  3  system  can  be  read  directly  by  depressing  the 
key  designated  as  A  L,  I,  No.  3. 

The  key  designated  as  No.  2  controls  the  connecting  wires  from  the 
ventilating  air-circuit,  and  by  depressing  this  key  the  temperature  dif- 
ferences between  the  ingoing  and  outcoming  air  are  noted  directly,  not 
as  absolute  temperature  measurements,  but  rather  as  an  indication  of 
the  necessity  for  warming  or  cooling  the  entering  air  to  adjust  its  tem- 
perature to  that  of  the  air  leaving  the  calorimeter  chamber. 

It  is  thus  seen  that  eight  keys  control  the  temperature  indications  of 
the  sections  of  the  thermal  junction  circuits,  and  that  three  keys  indi- 
cate temperature  conditions  respectively  in  the  whole  of  system  No.  i , 
the  whole  of  system  No.  3,  and  the  air  current.  For  the  indication  of 
these  temperature  conditions,  therefore,  eleven  keys  are  employed. 

The  connections  shown  by  the  wires  in  figure  42  can  be  followed 
more  exactly  by  the  plan  of  wiring  given  in  figure  43.  This  diagram 
can  be  compared  advantageously  with  the  view  of  the  switch  given  at 
the  left  in  figure  40,  as  the  diagrammatic  features  of  the  plan  of  wiring 
are  made  to  correspond  very  closely  with  the  exact  location  of  the  dif- 
ferent parts  of  the  switch  proper.  For  example,  the  two  coils  wound 
on  hard-rubber  spools  and  fastened  to  the  switch  by  screws  through  the 
center  of  the  spool,  which  are  shown  in  figure  40  at  the  top,  correspond 
to  the  two  coils  marked  2o-ohm  res.  on  the  diagram.  The  two  iron 
cups  which  are  filled  with  mercury  when  the  switch  is  in  use,  and  in 
which  the  galvanometer  terminals  are  immersed,  are  between  these  two 
coils,  while  the  iron  post  from  which  wires  pass  to  each  of  the  2o-ohm 
coils  is  between  the  galvanometer  connections,  exactly  in  the  middle  of 
the  upper  portion  of  the  switch.  The  two  wires  leading  from  the  gal- 
vanometer can  readily  be  traced  on  figure  43  to  these  two  iron  cups. 
It  can  be  seen  further  that  one  of  the  wires  from  the  battery  connects 
directly  with  the  iron  post  between  the  galvanometer  cups,  which  corre- 
sponds to  point  B'  in  figure  44  beyond. 

On  each  side  of  the  circle  designating  the  galvanometer  is  placed  a 
diagram  of  a  thermal  junction  system,  that  corresponding  to  the  inner 
metal- wall  system,  i.  e.,  No.  i,  on  the  left,  and  that  corresponding  to 
the  outer  system,  i.  <?.,  No.  3,  on  the  right.  Furthermore,  the  connec- 
tions of  the  separate  sections,  T,  U,  L,  B,  are  shown  for  each  system. 
Immediately  above  system  No.  i  is  the  representation  of  system  No.  2, 


A    RESPIRATION    CALORIMETER. 


or  that  in  the  ventilating  air  current.  It  will  be  noticed  that  systems 
No.  i  and  No.  2  unite  at  the  left  of  T  in  system  No.  i ,  and  thus  one 
wire  serves  for  the  return  from  both  systems. 

The  connections  between  the  several  thermal  junction  systems  and 
the  galvanometer  are  relatively  simple  ;  it  is  with  the  bridge  system  for 
temperature  measurements  that  the  electrical  connections  are  the  most 
complicated.  For  these  measurements  a  type  of  Wheatstone  bridge, 
illustrated  by  the  diagram  in  figure  44,  is  used. 

In  the  simple  form  of  Wheatstone  bridge  shown  in  figure  44  there 
are  in  fact  four  parts — two  2O-ohm  resistance  coils,  a  standard  resist- 
ance, and  the  coil  of  copper  wire  whose  temperature  fluctuations  (varia- 
tions in  resistance)  are  to  be  measured. 
The  battery  is  connected  at  the  two 
points  B'  and  B".  The  galvanometer 
connections  are  made  at  G'  and  G". 

The  two  20- ohm  resistance  coils  A 
and  B  are  made  of  a  form  of  wire  that 
has  no  temperature  coefficient,  i.  e., 
there  are  no  changes  in  electrical  con- 
ductivity due  to  changes  in  temper- 
ature. These  two  coils  are  calibrated 
with  the  greatest  accuracy,  so  that  the 
resistance  of  the  coils  and  connections 
between  B'  and  G'  is  exactly  equal  to 
those  between  B'  and  G";  thus  A  and  B 
correspond  to  the  proportional  arms  of 
a  Wheatstone  bridge.  These  two  coils 
are  shown  in  the  diagram,  figure  43, 
being  marked  2O-ohm  res.  Their  position  on  figure  40  is  likewise  clearly 
seen.  The  iron  post  between  these  two  coils  corresponds  to  the  point  B' 
of  figure  44.  The  points  B"  and  G'  and  G"  are  not  so  readily  discerned 
on  the  drawing  in  figure  43,  owing  to  the  complex  nature  of  the  elec- 
trical connections. 

The  other  two  arms  of  the  Wheatstone  bridge  (fig.  44)  are  com- 
posed of  a  standard  coil,  D,  made  of  wire  similar  to  that  used  in  coils 
A  and  B  and  having  approximately  20  ohms  resistance.  This  coil  is 
used  for  comparison  with  the  unknown  resistance  of  the  copper  ther- 
mometer coil  and  connections,  which  correspond  to  coil  C  in  figure  44. 
As  this  coil  (for  example,  the  copper  thermometer  used  for  measuring 
the  temperature  fluctuations  of  the  air  in  the  calorimeter  chamber) 
changes  in  resistance,  and  obviously  may  rarely  be  exactly  equal  in 
resistance  to  coil  D,  there  is  a  disturbance  of  the  equilibrium  of  resist- 


FIG.  44. — Diagram  of  simple  form  of 
Wheatstone  Bridge.  A  current  from  a 
battery  passes  through  an  adjustable 
resistance  and  connects  with  the  bridge 
at  points  B'  and  B".  When  all  arms  of 
the  bridge  are  proportional,  no  current 
flows  through  the  galvanometer  G.  If 
C  is-  greater  or  less  in  resistance  than  D, 
the  current  passes  through  G. 


THE   CALORIMETER  SYSTEM   AND   MEASUREMENT   OF   HEAT.       145 

ances  in  the  two  arms  of  the  bridge,  C  and  D,  and  consequently  a  small 
current  of  electricity  passes  through  the  galvanometer.  The  current 
may  pass  from  G'  to  G"  if  the  coil  C  has  a  greater  resistance  than  D,  or 
it  may  pass  from  G"  to  G'  if  the  coil  C  has  less  resistance  than  coil  D. 
It  is  important  to  bear  in  mind  that  the  resistances  of  the  coils,  plus  the 
resistance  of  connecting  wires,  must  be  taken  into  consideration  rather 
than  the  resistance  of  the  coils  alone.  Unless  the  resistance  of  the  coil 
C  and  all  its  connections  with  the  points  G'  and  B"  (fig.  44)  is  exactly 
equal  to  the  resistance  of  the  coil  D  and  its  connections  with  the  points 
G"  and  B",  a  current  of  electricity  will  pass  through  the  galvanometer. 

In  the  ordinary  form  of  Wheatstone  bridge,  provision  is  made  for 
altering  the  resistance  of  coil  D  until  the  equilibrium  is  again  established, 
the  degree  of  alteration  in  coil  D  being  an  index  of  the  resistance  change 
(temperature  change)  in  coil  C.  The  so-called  "  slide-wire  "  form  of 
Wheatstone  bridge  alters  the  position  of  the  point  B",  thus  varying  the 
total  resistances  between  B"  and  G',  and  B"  and  G",  until  the  equilib- 
rium is  established  and  no  current  flows  through  the  galvanometer. 
With  either  of  these  two  methods  of  resistance  adjustment,  elaborate 
and  delicate  apparatus  is  required  and  the  continuous  use  of  such  instru- 
ments is  accompanied  by  a  constantly  increasing  inaccuracy  in  their  use, 
due  to  the  wearing  of  parts.  In  the  mercury  contact  switch  and  bridge 
described  here,  the  use  of  a  Wheatstone  bridge  and  resistance  box,  or  a 
slide-wire  bridge,  is  obviated. 

If  in  the  system  shown  in  figure  44  the  resistance  of  coil  C  varies 
and  is  not  identical  with  coil  D,  a  current  will  pass  through  the  gal- 
vanometer and  produce  a  deflection.  This  deflection  will,  in  general, 
be  nearly  proportional  to  the  amount  of  current  flowing  through  the 
galvanometer,  and,  as  the  current  is  equal  to  the  electro-motive  force 
divided  by  the  resistance,  it  follows  that  with  a  constant  electro-motive 
force  the  current  varies  inversely  as  the  resistance.  Assuming  that 
the  resistance,  coil  C  (fig.  44),  at  a  given  temperature  is  such  as  to 
cause  a  current  of  electricity  to  pass  through  the  galvanometer  and 
produce  a  deflection  of  100  mm.  on  the  scale,  if  the  resistance  of  the  coil 
C  is  now  decreased  a  larger  current  will  pass  through  the  galvanometer 
and  the  deflection  will  become  larger.  Conversely,  if  the  resistance  of 
C  increases,  a  smaller  current  of  electricity  will  flow  through  the  galva- 
nometer and  the  deflections  will  grow  smaller.  If,  now,  the  resistance 
of  C  is  increased  further,  there  will  be  a  point  at  which  the  resistance 
of  C  is  equal  to  D  and  no  current  will  pass  through  the  galvanometer, 
and  if  the  resistance  is  still  more  increased,  the  current  will  tend 
to  flow  through  the  galvanometer  in  the  opposite  direction,  and  con- 
stantly increasing  deflections,  though  in  the  opposite  direction  from 


146  A    RESPIRATION   CALORIMETER. 

those  at  the  beginning,  will  be  obtained.  Obviously,  the  direction  of 
the  current  through  the  galvanometer  and  the  direction  of  the  deflection 
for  increasing  or  diminishing  resistances  in  C  depend  upon  the  direction 
of  the  current  from  the  battery  and  also  upon  the  connections  through  the 
galvanometer  terminals,  for  by  interchanging  the  wires  leading  from 
the  galvanometer  to  G'  and  G"  the  current  through  the  galvanometer 
may  be  made  to  pass  in  the  opposite  direction. 

Of  the  four  resistances  in  the  bridge  system,  but  one  is  affected  by 
temperature  changes,  i.  <?. ,  that  composed  of  the  copper  coils  ;  hence  any 
differences  in  the  deflection  of  the  galvanometer  may  be  ascribed  directly 
to  variations  in  resistance  of  the  copper  coil,  provided  the  electro- motive 
force  of  the  battery  remains  constant.  To  insure  a  constant  electro- 
motive force,  we  have  relied  upon  the  establishment  of  an  arbitrarily 
adjusted  bridge  system,  in  which  the  coils  C  and  D  are  slightly  out  of  pro- 
portion, i.  e. ,  coil  C  has  a  somewhat  lower  resistance  than  coil  D.  Both 
coils  (C  and  D)  in  this  system  are  made  of  wire  with  zero  temperature 
coefficient.  These  coils  are  mounted  on  the  mercury  contact  switch  (fig. 
40),  one  on  each  side  of  the  rows  of  mercury  cups  in  the  oak  base  and 
about  midway  of  the  sides.  The  coils  are  similar  in  form  to  the  two  20- 
ohm  coils  mentioned  before,  and  while  one  has  a  resistance  of  exactly  20 
ohms,  the  other  is  a  small  fraction  of  an  ohm  lower  in  resistance.  Inas- 
much as  these  coils  belong  to  a  bridge  system  that  is  used  to  standardize 
the  electro-motive  force  from  the  battery,  they  are  called  standard  coils, 
or  standard  resistances,  and  on  figure  43  they  are  marked  St'd  res. 

With  the  bridge  system  thus  arranged,  the  closing  of  the  battery  and 
galvanometer  circuits  should  result  in  a  deflection  of  the  galvanometer, 
owing  to  the  inequality  of  arms  C  and  D  of  the  bridge.  The  deflection 
of  the  galvanometer  is  then  approximately  proportionate  to  the  electro- 
motive force,  and  by  adjusting  the  number  of  cells  of  the  battery  and 
varying  the  resistance  in  the  battery  circuit  it  is  possible  to  produce  a 
deflection  of  any  definite  magnitude.  Since  all  coils  are  of  wire  with 
zero  temperature  coefficient,  no  changes  in  temperature  will  affect  the 
bridge  system,  and  the  amount  of  current  necessary  to  produce  a  deflec- 
tion of  100  mm.,  for  example,  will  be  constant,  provided  there  are  no 
variations  in  the  galvanometer  constant.  This  latter  factor  can  be  tested 
readily,  and  in  fact  varies  but  slightly,  so  that  we  have  by  this  bridge 
system  an  excellent  method  of  compensating  for  variations  in  the  electro- 
motive force  of  the  battery.  As  a  source  of  current,  we  use  ordinary 
dry  cells,  with  a  small  variable  resistance  in  series  with  them.  With 
this  arrangement  and  with  the  connections  as  now  made,  the  amount 
of  current  required  to  produce  a  deflection  of  1 20  mm.  is  used  as  the 
standard  for  all  our  work.  Inasmuch  as  the  temperature  of  the  cal- 


THE   CALORIMETER  SYSTEM   AND   MEASUREMENT  OP   HEAT.       147 

orimeter  room  is  always  of  such  uniformity  as  to  cause  only  slight  vari- 
ations in  the  electro-motive  force  of  the  batteries,  small  alterations  in  the 
variable  resistance  serve  to  keep  the  standard  current  well  in  hand. 
Variations  from  hour  to  hour  rarely  amount  to  more  than  2  or  3  mm. 
on  a  deflection  of  1 20  mm.  This  method  of  obtaining  a  constant  current 
is,  for  the  purpose  of  this  research,  sufficiently  accurate  and  on  the 
whole  distinctly  preferable  to  the  use  of  a  standard  cell. 

The  adaptation  of  the  mercury  contact  to  this  form  of  bridge  is  shown 
in  figure  43.  By  depressing  the  key  marked  S  the  copper  links  enter 
the  mercury  in  the  cups  in  such  a  manner  that  the  bridge  and  battery 
circuits  are  made  before  the  galvanometer  circuit.  In  this  key  it  is 
necessary  to  have  five  mercury  cups  instead  of  four,  as  in  the  keys 
connecting  the  thermal  junction  systems.  The  fifth  mercury  cup  is 
made  outside  of  the  square  inclosing  the  regular  cups,  and  is  seen  at 
the  right,  immediately  in  line  with  the  standard  resistance  coil  in  fig- 
ure 40.  The  fact  that  these  bridge  systems  were  added  to  the  mercury 
contact  switch  after  it  was  first  built  explains  the  irregularity  of  the 
position  of  the  extra  mercury  cups,  not  only  in  this  standard  circuit, 
but  also  in  the  four  bridge  circuits  controlled  by  the  four  keys  on  the 
bottom  row. 

The  flow  of  the  current  through  the  different  connections,  when  the 
key  is  depressed,  may  be  followed  very  readily  if  it  is  borne  in  mind  that 
all  the  copper  links  connect  cups  with  those  that  are  immediately  above. 
On  the  whole  switch  there  is  but  one  exception  to  this  rule,  and  that 
is  the  connection  for  the  battery  circuit  for  the  standard  system.  Here 
the  copper  link  connects  the  extra  mercury  cup  with  the  nearest  cup. 

In  figure  40  the  top  of  the  switch  at  the  right  is  removed  and  shown 
in  such  a  position  that  were  it  brought  over  like  the  cover  of  a  book 
the  copper  keys  would  fall  over  the  proper  mercury  cups.  Hence  it 
can  be  seen  that  the  two  upper  rows  are  for  the  cups  connecting  with 
the  two  thermal  junction  systems,  while  the  first  key  on  the  next  to  the 
lower  row  corresponds  to  the  standard  bridge  system.  Indeed,  the 
copper  link  extending  on  one  side  is  clearly  seen.  This  link  dips  into 
the  extra  mercury  cup.  The  four  lower  keys,  each  with  one  or  more 
extension  links,  belong  to  the  four  other  bridge  systems. 

Of  these  four  systems,  one  controls  the  measurement  of  temperature 
changes  in  the  copper  thermometer  suspended  in  the  air  in  the  calo- 
rimeter chamber.  This  is  designated  as  system  No.  5,  and  is  controlled 
by  the  lower  left-hand  key  (fig.  43).  The  standard  coil  of  zero  tem- 
perature coefficient  wire  used  for  comparison  with  the  copper  ther- 
mometer No.  5,  i.  e. ,  the  coil  corresponding  to  D  in  the  bridge  system 
(fig.  44),  is  wound  on  a  small  hard-rubber  spool,  and  is  provided  with 


148  A   RESPIRATION   CALORIMETER. 

two  heavy  copper  terminals,  which  can  be  dipped  in  the  iron  mercury- 
cups.  Four  of  these  coils,  corresponding  to  the  four  bridge  systems, 
are  shown  immediately  in  front  of  the  switch  in  figure  40.  They  are 
shown  in  position  in  figure  41.  The  terminals  of  the  coil  for  system 
No.  5  are  slipped  through  two  hard-rubber  bushings  hi  the  cover,  and 
extend  beneath  the  cover  far  enough  to  have  their  lower  ends  well 
immersed  in  mercury  in  two  iron  cups  similar  to  those  used  for  the 
galvanometer  terminals.  Those  for  system  No.  5  are  at  the  left  and 
near  the  top  of  the  switch,  as  shown  in  figure  40.  A  line  terminating 
in  arrow-heads  and  broken  by  the  designation  No.  5  shows  in  figure  43 
the  position  of  these  cups  and  the  connections  with  their  lower  ends. 
The  iron  mercury-cups,  as  well  as  the  iron  posts  for  the  battery  and 
bridge  connection  previously  mentioned  (see  p.  143),  are  provided  on  the 
under  side  with  hexagonal  nuts,  which  are  used  to  insure  the  best  elec- 
trical contact  for  the  various  parts  of  the  bridge  system.  These  nuts 
and  the  wiring  from  several  of  the  iron  cups  and  posts  are  shown  in 
figure  42.  As  can  be  seen  by  a  comparison  with  the  direction  of  the 
bundle  of  wires  extending  outward  from  one  side,  the  switch  has  been 
tipped  forward  through  180°  from  the  position  in  figure  40  to  give  the 
view  in  figure  42  ;  consequently  the  three  nuts  at  the  bottom  of  figure 
42  correspond  in  figure  40  to  the  two  galvanometer  terminal  mercury 
cups  and  the  iron  post  connecting  with  the  battery. 

Although  the  hexagonal  nuts  aid  in  making  a  good  contact,  the  con- 
nections for  all  the  bridge  systems,  especially  the  connections  which,  if 
defective,  would  disturb  the  equilibrium  of  either  arm  of  the  bridge, 
are  further  insured  by  having  soldered  joints.  All  connections  between 
the  iron  mercury-cups  and  the  calorimeter  chamber  are  made  of  very 
heavy  (No.  10)  copper  wire  to  eliminate  the  effect  of  temperature 
fluctuations  other  than  those  in  the  thermometer  coils. 

The  key  controlling  the  temperature  measurements  of  the  copper 
thermometers  which  indicate  the  temperature  of  the  copper  wall,  No. 
7,  is  in  the  bottom  row  (fig.  43),  at  the  extreme  right.  The  compari- 
son coil  dips  in  two  iron  cups  filled  with  mercury.  These  cups  are  at 
the  right  of  the  switch,  in  a  position  corresponding  to  that  occupied  by 
the  comparison  coil  No.  5.  The  line  terminating  in  arrow-heads  is 
broken  by  the  designation  No.  7. 

The  key  marked  R  controls  the  temperature  measurement  of  a  cop- 
per coil  used  for  obtaining  the  rectal  temperature  of  the  subject  of  the 
experiment.  This  thermometer  is  described  in  detail  elsewhere.  (See 
p.  156.)  The  comparison  coil  for  R  is  immediately  at  the  left  of  the 
keys  A  I,  I,  No.  i  and  No.  5. 


THE   CALORIMETER   SYSTEM,  AND   MEASUREMENT  OF   HEAT.       149 

The  key  marked  W  is  not  as  yet  in  practical  use.  Experiments  are 
in  progress  to  utilize  this  method  of  temperature  measurement  to  obtain 
the  differences  in  temperature  of  the  ingoing  and  outcoming  water  cur- 
rents, temperature  differences  now  measured  by  mercurial  thermom- 
eters. (See  p.  133.)  The  coil  W  is  immediately  at  the  right  of  the 
keys  marked  S  and  No.  7. 

With  the  large  area  of  wire  exposed  in  the  copper  thermometer  coils 
No.  5  and  No.  7,  and  the  consequent  rapid  radiation,  we  have  found 
that  the  slight  amount  of  current,  0.03  ampere,  produces  no  appre- 
ciable local  heating  effect  in  the  coils ;  hence  the  reading  of  the  gal- 
vanometer may  be  taken  with  the  circuit  closed  and  after  the  deflec- 
tion has  become  constant.  The  method  of  reading  the  deflection  ob- 
tained when  the  R  coil  is  used  is  that  of  observing  the  amplitude  of 
the  first  swing.  As  the  coil  for  the  R  thermometer  is  compactly  wound, 
and  therefore  does  not  radiate  heat  readily,  the  passage  of  the  current 
through  it  heats  the  coil,  giving  rise  to  erroneous  readings.  The 
amplitude  of  the  first  swing  has  been  found  to  be  sufficiently  accurate 
for  these  readings,  and  the  rectal  thermometers  are  calibrated  to  be  read 
under  these  conditions. 

At  the  upper  left-hand  side  of  figure  43  the  various  coils  and  their 
connections  with  the  switch  are  shown.  It  is  thus  seen  that  coils  No. 
5,  No.  7,  and  R  all  have  a  common  return  wire  from  the  calorimeter 
chamber. 

The  connections  for  the  coils  for  the  bridge  system  inside  the  calo- 
rimeter— i.  e.,  copper  thermometer  for  the  air  (No.  5),  thermometer 
for  the  copper  walls  (No.  7),  and  the  rectal  thermometer — are  con- 
ducted from  the  mercury  switch  through  a  cable  having  a  number  of 
strands  of  heavy  flexible  wires  to  a  plug  switch  fastened  to  the  copper 
wall  of  the  calorimeter.  This  cable  is  seen  in  figures  29  and  30,  while 
the  location  of  the  plug  switch  is  seen  at  M,  figure  33.  The  connections 
for  the  bridge  systems  corresponding  to  No.  5,  No.  7,  and  R  are  made 
by  inserting  tapered  plugs  into  the  different  sections  of  this  switch. 
Other  sections  (there  are  ten  in  all)  can  be  used  for  other  electric  cir- 
cuits, such  as  the  telephone,  wires  for  electrical  check  experiments, 
and  connections  for  the  bicycle  ergoineter  (see  p.  164),  but  they  are 
connected  with  much  smaller  (No.  18)  wires  with  a  set  of  switches 
under  the  edge  of  the  observer's  table.  (See  fig.  37.) 

In  the  connections  between  the  thermal  junction  system  and  the  gal- 
vanometer, relatively  large  changes  in  resistance  in  the  contacts  are 
without  effect  on  the  deflection  of  the  galvanometer  ;  but  it  is  readily 
seen  that  with  the  bridge  systems  the  matter  is  very  different.  Here 
the  mercury  contacts  become  a  part  of  the  connection  between  G'  and 


150  A   RESPIRATION   CALORIMETER. 

B",  and  G"  and  B",  of  figure  44  ;  hence  the  necessity  for  the  reliability 
of  these  connections.  With  clean  mercury  and  good  copper  links,  the 
connections  are  all  that  could  be  desired. 

This  switch  has  been  in  constant  use  three  years  and  has  given 
excellent  satisfaction.  Inasmuch  as  all  temperature  measurements  are 
relative,  not  absolute,  and  the  variations  in  temperature  are  slight,  it 
can  readily  be  seen  that  this  form  of  bridge  is  especially  well  suited  for 
experimental  work  of  this  nature.  The  sensitiveness  is  all  that  could 
be  desired,  since  with  the  present  adjustment  60  deflections  (millimeters) 
correspond  to  i°  C. ;  hence  readings  of  0.01°  are  readily  obtained,  an 
accuracy  sufficient  at  present  for  experiments  with  the  respiration  calo- 
rimeter. That  some  form  of  potentiometer  could  be  used  for  this  work 
with  good  results  is,  of  course,  not  to  be  doubted,  but  the  compact  form 
of  this  switch  and  bridge  leaves  little  to  be  desired  for  the  purposes  for 
which  it  was  devised. 

DETERMINATION   OF  THE   QUANTITY   OP   HEAT   ELIMINATED. 

It  has  been  shown  that  heat  is  regularly  carried  out  of  the  calorim- 
eter chamber  in  two  ways — partly  as  latent  heat  of  water  vapor  in  the 
air  current,  but  chiefly  as  sensible  heat  taken  up  by  a  current  of  water 
circulating  in  the  heat-absorbers.  Theoretically,  the  sum  of  the  two 
quantities  of  heat  thus  removed  should  equal  the  total  amount  elim- 
inated within  the  chamber,  but  in  actual  practice  various  corrections 
must  be  made  to  determine  the  actual  quantity  of  heat.  The  method 
of  computing  the  quantity  of  heat  removed  in  these  two  ways  and  the 
necessary  corrections  to  be  applied  remain  to  be  described. 

LATENT  HEAT  OF  WATER  VAPOR. 

The  quantity  of  heat  removed  from  the  chamber  in  water  vapor  is 
found  by  multiplying  the  quantity  of  water  collected  in  the  water-ab- 
sorbers by  the  factor  for  latent  heat  of  vaporization  of  water.  In  these 
experiments  the  factor  used  is  0.592  calorie  per  gram,  which  was  de- 
duced from  Regnault's  formula,  as  discussed  in  detail  elsewhere.1 

It  is  greatly  to  be  desired  that  this  factor  be  verified  by  investigations 
in  which  water  is  vaporized  under  the  conditions  that  obtain  during  an 
experiment  with  man  ;  but  although  considerable  preliminary  investi- 
gation of  this  nature  has  been  made,  we  have  no  results  that  warrant 
our  taking  other  than  the  commonly  accepted  figures  of  Regnault  for 
this  calculation.  Presumably  the  error  involved,  if  any,  is  not  very 
large.  Certainly  it  is  not  larger  than  the  probable  physiological  error 
in  experiments  of  this  type. 

1U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63,  p.  57. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT   OF   HEAT.       15! 

The  number  of  grams  of  water  removed  by  the  absorbers  multiplied 
by  the  above  factor  gives  the  number  of  calories  of  heat  escaping  from 
the  chamber  in  water  vapor.  To  obtain  the  total  quantity  of  heat 
involved  in  the  vaporization  of  water,  however,  it  is  necessary  to  make 
allowance  for  the  latent  heat  of  water  vapor  still  remaining  in  the 
chamber,  the  correction  being  added  or  subtracted  according  to  whether 
the  amount  of  residual  vapor  at  the  end  is  larger  or  smaller  than  that 
present  at  the  beginning  of  the  experimental  period. 

SENSIBLE  HEAT  REMOVED  IN  THE  WATER  CURRENT. 
UNIT  OF  HEAT. 

The  ordinary  definition  of  the  large  calorie  is  the  quantity  of  heat 
required  to  raise  the  temperature  of  i  kg.  of  water  i°  C.  This,  how- 
ever, is  only  approximately  correct,  because  the  specific  heat  of  water 
varies  with  the  temperature.1  It  is  therefore  necessary  to  define  the 
unit  of  heat  somewhat  more  exactly. 

In  experiments  the  temperature  of  the  calorimeter  chamber  is  main- 
tained very  constant  at  20°  ;  hence  the  specific  heat  of  water  at  20°  is 
taken  as  the  standard  ;  and  the  calorie  here  used  is  the  quantity  of  heat 
necessary  to  raise  a  kilogram  of  water  from  19.5°  to  20.5°. 

CALCULATION   OF  THE  QUANTITY  OF    HEAT  MEASURED. 

The  weight  of  the  water  determined  by  the  water-meter,  multiplied 
by  the  difference  between  the  temperature  of  the  water  as  it  enters  and 
that  as  it  leaves  the  chamber,  gives  the  quantity  of  heat  as  measured  at 
the  mean  between  the  temperatures  of  the  ingoing  and  outgoing  water. 
According  to  the  explanation  given  above,  however,  this  must  be  cor- 
rected for  the  difference  between  the  specific  heat  of  the  water  at  this 
mean  temperature  and  that  at  20° .  The  latter  value  is  designated  as  heat 
measured  in  terms  of  C.^  ;  the  former  value  is  designated  as  heat  measured 
in  terms  of  Ct,  in  which  t  is  any  temperature  other  than  that  of  20°. 

In  finding  the  true  value  of  Ct,  it  is  necessary  to  know  the  mean 
specific  heat  of  water  for  the  range  of  temperature  employed  in  any 
given  period.  The  temperature  of  the  ingoing  water  is  sometimes  as 
low  as  i°  ;  that  of  the  outgoing  water  is  rarely  above  15°,  and  more 
frequently  not  far  from  10°.  If,  for  example,  the  water  enters  the  cal- 
orimeter at  2°,  a  condition  that  is  very  common  during  the  hard- work 

1  The  results  of  a  large  number  of  experiments  on  the  specific  heat  of  water  at 
different  temperatures  have  been  discussed  in  considerable  detail  in  another  publi- 
cation (U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63,  p.  55).  From  a 
table  there  given  showing  the  specific  heat  of  water  at  different  temperatures  and 
referring  to  that  at  20°  as  a  unit,  it  is  seen  that  the  specific  heat  of  water  at  o°  is 
1.0090;  at  5°,  1.0056;  at  10°,  1.0029;  at  J50>  i.ooio.  The  difference  between  CM 
and  C0  is  one  of  nearly  i  per  cent. 


152  A   RESPIRATION   CALORIMETER. 

experiments,  and  leaves  the  chamber,  after  having  passed  through  the 
absorbing  pipes,  at  12°,  the  result  will  be  in  terms  of  C(z-i2)  or  in  terms 
of  the  mean  calorie  from  2°  to  12°.  From  the  table  above  referred  to 
it  is  found  that  the  specific  heat  at  2°  is  1.0076  and  at  12°,  1.0020. 
The  average  of  these  two  is  1.0047.  This  variation  is  approximately 
0.5  per  cent.  Since  the  accuracy  of  the  calorimetric  measurements  is 
considerably  within  i  per  cent,  it  is  evident  that  the  correction  above 
suggested  must  be  applied. 

In  making  the  correction,  the  quantity  of  heat  measured  in  terms 
of  Ct  is  multiplied  by  the  specific  heat  of  water  at  Ct  referred  to  that 
at  CM  as  a  standard. 

CORRECTIONS  TO  MEASUREMENTS  OF  HEAT. 

As  explained  above,  to  obtain  the  true  final  measurement  of  heat, 
allowance  must  be  made  for  certain  quantities  of  heat  introduced  or 
removed  in  various  ways.  The  different  corrections  to  be  made  are  dis- 
cussed in  the  following  sections. 

THE  HYDROTHERMAL  EQUIVALENT  OF  THE  CALORIMRTER. 

With  the  heat- regulating  devices  previously  described,  it  is  in  gen- 
eral not  at  all  difficult  to  control  the  temperature  of  the  calorimeter 
within  very  narrow  limits  ;  but  there  are  times  when  the  calorimeter 
system,  as  a  whole,  may  have  a  different  temperature  at  the  end  of  a 
period  than  at  the  beginning,  and  there  may  be  accordingly  either  a 
storage  or  a  loss  of  heat  in  the  system.  Obviously,  in  accurate  experi- 
menting, especially  in  short  periods,  it  is  necessary  to  know  the  actual 
amount  of  heat  thus  stored  or  lost.  This  involves  a  knowledge  of  the 
hydrothermal  equivalent  of  the  calorimeter,  since  the  mass  of  material 
thus  raised  or  lowered  in  temperature  must  be  known  and  expressed  in 
its  equivalent  weight  of  water. 

With  a  calorimeter  of  this  type  of  construction  it  is  not  an  easy  matter 
to  determine  the  hydrothermal  equivalent  with  great  accuracy.  The 
inner  copper  wall  is  heated  by  the  heat  radiating  from  the  subject. 
The  outer  zinc  wall  is  heated  by  the  electrical  current  in  the  air-space 
surrounding  it.  If  the  chamber  undergoes  a  certain  rise  in  tempera- 
ture, it  is  difficult  to  state  exactly  what  proportion  of  the  heat  given  off 
by  the  subject  is  utilized  in  raising  the  temperature  of  the  copper  wall 
and  what  proportion  is  utilized  in  raising  the  temperature  of  the  zinc 
wall,  for  while  there  is  obviously  a  distinct  period  during  which  the 
copper  wall  is  warmer  than  the  zinc  wall,  it  is  by  no  means  absolutely 
certain  that  when  the  temperature  is  rising  all  the  heat  from  the  man's 
body  escapes  to  the  zinc  wall  before  the  electrical  heating  circuit  begins 


THE   CALORIMETER   SYSTEM.  AND   MEASUREMENT   OF   HEAT.       153 

to  warm  up  this  wall.  Conversely,  if  there  be  a  fall  in  temperature, 
it  is  possible  that  the  reverse  may  result. 

Inasmuch  as  with  experienced  observers  the  variations  in  tempera- 
ture are  very  slight,  and  as  the  press  of  experimental  work  has  pre- 
vented our  making  further  determinations  of  the  hydrothermal  equiva- 
lent, we  have  used  in  all  the  investigations  so  far  the  results  of  an 
experiment  published  1  in  1899.  In  this  test  the  calorimeter  was  held 
at  a  constant  temperature  for  several  hours  ;  a  small  electrical  current 
was  then  passed  through  a  resistance  coil  in  it  for  two  hours.  During 
this  period  of  time  especial  pains  were  taken  to  keep  the  thermal  junc- 
tion circuits  in  the  metal  walls  at  equal  temperatures,  and  as  a  result, 
since  no  heat  was  allowed  to  pass  through  the  walls,  the  temperature 
of  the  calorimeter  slowly  rose.  At  the  end  of  two  hours  the  current 
was  stopped  and  the  calorimeter  allowed  to  assume  a  constant  tempera- 
ture. From  the  rise  in  temperature  and  the  amount  of  heat  generated 
by  the  electric  current,  it  was  calculated  that  the  apparatus  required 
about  60  large  calories  to  raise  its  temperature  i  °  ;  hence  its  hydro- 
thermal  equivalent  is  not  far  from  60. 

The  true  significance  of  this  factor  is  becoming  less  and  less  each  year 
as  the  experimental  skill  of  the  manipulators  increases.  It  is  our  pur- 
pose, however,  to  repeat  these  tests,  and  consider  a  fall  in  temperature  as 
well  as  a  rise  in  determining  exactly  the  hydrothermal  equivalent  of  the 
apparatus.  Suffice  it  to  say  that  for  the  fluctuations  ordinarily  occur- 
ring in  experimental  apparatus,  it  is  known  with  sufficient  accuracy. 

An  attempt  has  been  made  to  calculate  the  hydrothermal  equivalent 
from  the  weight  of  the  different  parts  of  the  apparatus  ;  but,  as  these 
weights  were  not  taken  at  the  time  the  apparatus  was  constructed  and 
the  quantity 'of  wood,  solder,  etc.,  involved  in  the  framework  is  not 
definitely  known,  these  results  are  not  at  present  available  for  use. 

CORRECTIONS   FOR   TEMPERATURE  OF   FOOD   AND  DISHES. 

In  order  to  compute  the  total  income  and  outgo  of  heat  from  the  cal- 
orimeter system,  it  is  necessary  to  know  the  temperature  of  all  articles 
passed  into  or  taken  out  of  the  calorimeter  chamber.  If  the  food,  drink, 
and  dishes  going  into  the  chamber  are  below  the  calorimeter  temper- 
ature, there  will  be  a  certain  amount  of  heat  absorbed  in  warming  the 
material  to  the  temperature  of  the  chamber;  and,  conversely,  if  any  of 
the  materials  are  warmer  than  the  interior  temperature,  they  will  grad- 
ually radiate  heat  until  they  assume  the  temperature  of  the  calorimeter. 
Similarly,  if  material  is  passed  out  of  the  chamber  at  a  higher  or  lower 
temperature,  there  is  a  loss  or  gain  of  heat. 

1  U.  S.  Dept.  of  Agr. ,  Office  of  Experiment  Stations  Bull.  63,  p.  44. 


154  A    RESPIRATION    CALORIMETER. 

Theoretically,  all  material  should  enter  or  leave  the  calorimeter  cham- 
ber at  the  inside  temperature,  but  in  practice  it  has  been  found  impos- 
sible to  do  this  ;  hence  a  correction  is  necessary. 

From  the  weights  of  all  materials  entering  the  chamber  and  their 
specific  heats,  their  hydrothermal  equivalent  can  be  readily  calculated, 
which,  multiplied  by  the  difference  in  temperature,  gives  the  amount 
of  heat  added  to  or  lost  from  the  chamber.  These  corrections  are  made 
for  each  experimental  period,  the  data  being  determined  directly  from 
a  record  sheet  posted  near  the  food  aperture. 

ADIABATIC   COOLING   OP   GASES. 

With  fluctuations  in  barometric  pressure,  the  air  inside  the  calorim- 
eter expands  or  contracts,  and  consequently  liberates  or  absorbs  heat 
according  to  the  well-known  laws  of  adiabatic  cooling.  In  considera- 
tion of  the  large  volume  of  air  in  the  calorimeter,  the  probable  effect 
of  fluctuations  in  barometric  pressure  on  the  amount  of  heat  liberated 
during  a  given  period  has  to  be  considered. 

From  data  furnished  by  the  chief  of  the  Weather  Bureau,1  it  has 
been  computed  that  a  maximum  fall  of  10  mm.  in  the  barometer  is 
accompanied  by  a  cooling  of  1.1°,  which  is  equivalent  to  1.624  large 
calories,  or  0.1624  calorie  per  millimeter.  This  amount  of  heat  is 
absorbed  (rendered  latent)  as  the  barometer  falls,  and  liberated  as  the 
barometer  rises. 

Save  in  very  exceptional  fluctuations  in  the  barometer,  this  correc- 
tion does  not  have  to  be  taken  into  consideration,  and  thus  far  has  not 
been  necessary.  It  is  possible,  however,  that  in  rest  or  fasting  experi- 
ments, in  which  the  amounts  of  heat  liberated  are  small,  this  correction 
may  amount  to  a  percentage  of  the  whole  so  large  that  it  should  be 
allowed  for. 

CORRECTION   FOR  HEAT   ABSORBED    BY   BED  AND   BEDDING. 

When  the  subject  retires  (at  1 1  p.  m. ) ,  the  heat  radiated  from  the  body 
is  absorbed  by  the  bed  and  bedclothes  till  the  temperature  of  the  por- 
tions nearest  his  body  are  warmed  from  chamber  temperature  (20°)  to 
approximately  that  of  the  body  (35°).  As  a  result,  the  heat  measured 
from  ii  p.  m.  to  i  a.  m.  is  too  low.  On  the  other  hand,  when  the  sub- 
ject leaves  his  bed  (at  7  a.  m.),  the  bed  and  bedding  again  cool  down  to 
the  temperature  of  the  chamber,  and  the  heat  measured  from  7  a.  m.  to 
9  a.  m.  is  too  high.  In  determining  the  heat  output  by  periods,  correc- 
tion should  be  therefore  made  for  heat  stored  in  this  way.  The  data 
available  for  estimating  the  exact  amount  of  this  heat  are  by  no  means 

1  U.  S.  Weather  Bureau,  Report  (1899),  u,  p.  492. 


THE   CALORIMETER  SYSTEM   AND   MEASUREMENT  OF   HEAT.       155 

so  complete  as  could  be  desired.  A  tentative  figure,  which  is,  however, 
little  more  than  a  rough  estimate,  is  30  calories.  In  practice  it  has 
been  our  custom  to  add  30  calories  to  the  heat  measured  during  the 
period  from  1 1  p.  m.  to  i  a.  m. ,  and  to  deduct  30  calories  from  the  heat 
measured  during  the  period  from  7  a.  m.  to  9  a.  m.  following.  If  the 
subject  be  restless  or  uneasy  during  the  night,  so  that  bedding  is 
removed,  the  correction  is  of  course  affected,  and  such  condition  must 
be  considered  in  applying  the  correction. 

This  correction  applies  only  to  the  measurements  of  heat  for  different 
periods  of  the  day.  For  the  whole  day  the  two  corrections  are  com- 
pensating and  are  therefore  negligible. 

CORRECTION  FOR  CHANGE  OF  BODY  TEMPERATURE  AND  BODY  WEIGHT. 

In  the  calculations  thus  far  outlined  it  has  been  assumed  that  the 
temperature  of  the  body  of  the  subject  has  been  constant  throughout 
an  entire  period,  and  that  there  has  been  no  gain  or  loss  of  body  weight. 
It  is  obvious,  however,  that  in  an  actual  experiment  either  or  both  of 
these  assumptions  may  be  incorrect.  Accurate  temperature  measure- 
ments show  a  considerable  variation  even  under  apparently  uniform 
conditions,  and  the  body  weight  undergoes  a  continual  loss  through  the 
elimination  of  body  carbon  and  hydrogen  as  carbon  dioxide  and  water 
vapor  by  the  lungs  and  skin,  besides  the  marked  gains  and  losses  fol- 
lowing the  intake  of  food  and  the  excretion  of  feces  and  urine. 

The  effect  of  such  fluctuations  may  be  that  of  either  increasing  or 
decreasing  the  amount  of  heat  measured  during  the  period.  Thus,  if 
the  body  weight  has  remained  constant,  but  the  body  temperature  has 
increased,  there  has  been  an  absorption  of  heat  by  the  body  which  has 
escaped  measurement.  An  amount  equivalent  to  the  gain  in  temper- 
ature multiplied  by  the  body  weight  and  the  specific  heat  of  the  body 
is  therefore  to  be  added.  On  the  other  hand,  a  fall  in  temperature 
would  give  a  correction  to  be  subtracted.  Similarly,  if  the  temperature 
remains  constant,  a  gain  in  weight  denotes  a  correction  to  be  added  to 
the  heat  measured,  since  with  this  gain  of  weight  a  certain  amount  of 
heat,  depending  upon  the  specific  heat  of  the  substance  gained  and  the 
difference  in  temperature  of  the  body  and  the  chamber,  has  been 
required  to  raise  the  substance  from  the  temperature  of  the  chamber  to 
that  of  the  body.  In  case  both  body  temperature  and  body  weight 
have  varied,  the  correction  may  be  either  positive  or  negative. 

In  practice,  readings  of  body  temperature  are  taken,  when  practi- 
cable every  four  minutes,  and  arrangements  are  such  as  to  permit  of 
weighing  the  subject  at  the  end  of  each  period  if  desired.  The  neces- 
sary corrections  may  then  be  applied. 


156  A    RESPIRATION   CALORIMETER. 

Measurements  of  body  temperature. — In  experiments  in  which  the  heat 
production  is  determined,  it  has  been  commonly  supposed  that  the  body 
temperature  at  any  given  hour  of  the  day  is  practically  the  same  from 
day  to  day.  Inasmuch  as  the  body  temperature  undergoes  a  daily 
fluctuation,  with  a  minimum  in  the  morning,  usually  between  2  and  4 
o'clock,  and  a  maximum  in  the  afternoon  about  5,  a  true  measure  of 
the  heat  production  by  short  periods  (two  or  three  hours)  can  only  be 
determined  by  making  corrections  for  changes  in  body  temperature  at  the 
beginning  and  end  of  any  given  period.  To  ascertain  these  fluctua- 
tions of  temperature,  a  special  form  of  thermometer,  based  on  variations 
in  electrical  resistance,  was  devised.  The  thermometer,  its  calibration 
and  method  of  use,  and  a  large  number  of  observations  made  with  it 
are  described  in  detail  elsewhere.1  An  illustration  of  the  apparatus  and 
a  brief  description  of  it  are  here  given. 


FIG.  45.— Rectal  Thermometer.  A  coil  of  fine  platinum  or  copper  wire  inclosed  in  a  pure  silver 
tube  is  connected  by  an  incandescent  lamp  cord  to  two  metal  plugs  which  fit  in  a  switch.  About 
20  cm.  of  the  other  end  is  covered  with  rubber. 

A  coil  of  fine  double-silk  covered  wire  (either  copper  or  platinum), 
having  a  resistance  of  about  20  ohms,  is  inclosed  in  a  small  silver 
tube  30  mm.  long  and  5  mm.  in  diameter.  The  two  ends  of  a  flex- 
ible cable  pass  through  a  hard-rubber  plug  in  the  end  of  the  silver 
tube  and  connect  with  the  coil.  A  piece  of  soft- rubber  tubing  is  slipped 
over  the  flexible  cable  and  the  ends  well  fastened  with  silk  and  shellac. 
The  thermometer  may  then  be  inserted  some  10  to  12  cm.  in  the  rectum 
and  worn  with  little  inconvenience  to  the  subject.  The  cable  is  connected 
with  the  plug  switch  and  the  variations  in  resistance  of  the  rectal  ther- 
mometer are  measured  by  one  of  the  bridge  systems  in  the  special  form 
of  mercury  switch  previously  described.  (Seep.  148.)  Fluctuations  of 
one-hundredth  of  a  degree  Centigrade  can  be  readily  determined, 
is  thus  possible  to  have  observations  of  the  body  temperature  of  the 
subject  within  the  respiration  chamber  recorded  independently  by  the 
observer  outside  of  the  chamber.  Observations  are  usually  made  every 
4  minutes. 

1  Archiv.  f.  d.  g.  Physiol.  (Pfluger),  1901,  88,  pp.  492-500,  and  1902,  90,  pp.  33-72. 


THE   CALORIMETER  SYSTEM  .AND   MEASUREMENT   OF   HEAT.       157 

Weighing  objects  inside  the  chamber. — Aside  from  the  variable  weight 
of  the  body  of  the  subject  of  the  respiration  calorimeter  experiments, 
there  is  a  continually  fluctuating  weight  of  the  absorber  system,  the  bed- 
ding, furniture,  and  clothing,  due  to  variations  in  water  content.  A 
number  of  preliminary  experiments,  made  several  years  ago  in  this 
laboratory,  to  attempt  to  determine  the  variations  in  weight  of  sheet 
copper  exposed  to  different  hygrometric  conditions,  gave  negative  re- 
sults, and  hence  it  has  been  assumed  that  any  changes  in  the  amount 
of  water  condensed  on  the  surface  of  the  metal  chamber  must  be  very 
slight  and  may  be  neglected  ;  but  we  have  found  repeatedly  that  wood 
and  textile  fabrics  absorb  an  appreciable  amount  of  water  which  must 
be  considered  in  accurate  work. 

There  is  not,  however,  much  wood  in  the  chamber.  A  wooden  chair 
is  used,  in  which  the  man  is  weighed,  and  there  is  some  woodwork  on 
the  bicycle  ergometer  and  telephone,  but  these  are  well  shellacked  and 
polished,  and  we  have  no  reason  to  believe  that  they  alter  in  weight, 
although  the  construction  of  the  apparatus  is  such  as  to  render  actual 
weighings  somewhat  difficult. 

With  the  clothing  and  bedding  of  the  subject,  we  have  conditions 
under  which  there  may  readily  be  wide  fluctuations  in  weight.  If, 
however,  provision  can  be  made  for  weighing  such  articles  accurately, 
the  fluctuations  in  weight  can  be  determined  and  a  correction  applied 
accordingly. 

The  large  differences  in  the  amount  of  water  condensed  on  the  ab- 
sorbing system  have  been  referred  to  on  pages  23  and  126.  In  order 
to  know  the  exact  amount  of  water  in  the  chamber  at  any  given  time, 
it  is  necessary  to  know  the  variations  in  weight  of  the  absorbing 
system. 

The  variations  in  weight  of  the  subject  are  of  special  significance  in 
their  use  as  a  check  on  the  oxygen  determinations,  for  if  we  have  the 
weight  of  the  income  of  food  and  drink,  the  weight  of  the  outgo,  and 
the  variations  in  weight  of  the  body  of  the  subject,  it  is  possible  to  cal- 
culate arithmetically  the  amount  of  oxygen  taken  out  of  the  air  by  the 
man.  In  considering  the  fluctuations  in  the  weight  of  the  subject, 
however,  it  is  impossible  to  distinguish  between  the  water  in  the  body 
of  the  subject  and  that  on  the  surfaces  of  metal,  or  absorbed  by  the 
woodwork,  clothing,  etc. ,  all  of  which  are  liable  to  changes  in  weight ; 
and  since  the  water  on  the  coat  of  the  subject  can  not  be  differentiated 
from  the  same  weight  of  water  in  the  body  of  the  subject,  it  is  there- 
fore necessary  to  know  not  only  the  changes  in  weight  of  the  body  of 
the  subject,  but  also  the  changes  in  weight  of  the  bedding,  absorber 
system,  etc.  Only  by  knowing  these  variations  in  weight  can  the 


158  A   RESPIRATION  CALORIMETER. 

changes  taking  place  in  the  water  content  of  the  body  be  stated  accu- 
rately. It  is  evident  further  that  inasmuch  as  it  is  impossible  to  dis- 
tinguish between  water  in  the  body  of  the  subject  and  the  water  on  the 
bedclothes,  it  is  useless  to  weigh  the  bedclothes  any  more  accurately 
than  the  weight  of  the  man's  body  can  be  obtained,  and  also  useless  to 
provide  for  the  weighing  of  the  bedclothes  if  the  man's  body  can  not 
be  weighed. 

In  the  earlier  experiments  we  endeavored  to  weigh  the  subject  by 
means  of  a  platform  balance  ;  but  though  the  balance  was  extremely 
sensitive  when  standing  on  the  laboratory  floor,  it  was  found  that  when 
placed  inside  of  the  calorimeter  chamber  the  inequalities  of  the  floor 
surface  were  such  as  to  make  accurate  weighing  practically  impos- 
sible, though  probably  the  error  was  not  greater  than  100  to  200  grams 
under  the  most  favorable  circumstances. 

Description  of  weighing  apparatus. — In  considering  any  method  for 
weighing  the  subject  inside  the  chamber,  it  was  seen  that,  to  be  of 
any  value,  the  weights  should  be  accurate  to  at  least  within  5  grams, 
since  5  grams  would  correspond  to  the  weight  of  about  3  liters  of  oxygen. 
Furthermore,  the  weighings  must  be  carried  out  fairly  rapidly,  and  what- 
ever apparatus  was  used  must  be  capable  of  sustaining  a  weight  equal 
to  that  of  the  body  of  the  subject.  It  was,  moreover,  deemed  highly 
important  to  devise  a  method  by  which  all  of  the  weighings  could,  if 
possible,  be  made  outside  of  the  respiration  chamber,  where  the  weights 
could  be  properly  checked  by  a  second  observer. 

The  space  between  the  ceiling  of  the  laboratory  and  the  top  of  the 
calorimeter  is  small,  but  it  was  possible,  by  going  to  the  floor  above 
and  cutting  through  the  ceiling,  to  arrange  a  platform  balance  imme- 
diately over  the  center  of  the  top  of  the  chamber.  A  hole  was  then  cut 
straight  down  through  both  top  panels  of  the  calorimeter  and  through 
the  double  wall  of  the  metal  chamber,  and  through  this  an  apparatus 
was  arranged  for  suspending  objects  within  the  chamber  from  the  plat- 
form scale.  The  arrangement  of  the  apparatus  is  shown  in  figure  46. 

A  copper  shoulder,  threaded  on  the  inside,  was  securely  soldered  to  the 
copper  wall  of  the  chamber.  A  long  fiber  tube  was  screwed  into  this 
wall  and  thus  gave  an  opening  in  the  wall  through  which  could  pass 
vertically  a  cord  or  rod  on  which  the  object  to  be  weighed  could  be 
suspended.  To  make  the  opening  continuous  to  the  upper  side  of  the 
ceiling  of  the  calorimeter  laboratory,  the  fiber  tube  was  lengthened  out 
by  screwing  a  brass  tube  to  its  end.  This  gave  a  straight  opening,  30  mm. 
in  diameter,  from  the  floor  above  down  into  the  calorimeter  chamber. 
It  was  well  adjusted  in  a  vertical  position  and  thus  permitted  the  suspen- 
sion of  a  weight  by  a  rod  without  having  the  rod  touch  the  sides  of  the 
tube. 


THE   CALORIMETER   SYSTEM  AND    MEASUREMENT   OF   HEAT.       159 

In  weighing  any  suspended  object,  some  up-and-down  motion  is  of 
course  necessary.  If  an  equipoise  were  used,  this  motion  would  extend 
through  several  inches,  but  if  a  platform 
balance  is  used,  it  may  be  cut  down  to  a 
small  fraction  of  an  inch.  Moreover,  a 
series  of  tests  showed  that  if  all  lateral 
motion  could  be  eliminated  it  was  pos- 
sible to  remove  the  hooks  fastened  to  the 
under  side  of  the  platform  and  designed 
to  prevent  lateral  motion  and  thus  ma- 
terially increase  the  sensitiveness  of  the 
balance. 

The  balance  in  use  is  of  the  Fairbanks 
platform  type,  designated  by  the  manu- 
facturers as  a  silk  platform  scale.  It  is 
graduated  to  10  grams  and  has  a  capacity 
of  150  kg.  It  was  put  in  place  exactly 
over  the  opening  through  the  floor  down 
into  the  calorimeter,  carefully  leveled  by 
placing  thin  strips  of  copper  under  each 
of  the  corners,  and  was  rigidly  fixed  in 
this  position.  A  hanger  was  constructed 
of  half-inch  pipe,  and  a  quarter-inch  rod 
attached  to  the  lower  part  of  the  hanger 
extended  through  the  opening  into  the 
calorimeter.  On  the  lower  end  of  this  rod 
was  attached  a  rubber  stopper  for  closing 
the  opening  when  the  weighing  is  com- 
pleted, and  a  stout  iron  ring  into  which 
various  supports  for  weighing  the  man 
and  other  objects  could  be  hooked.  The 
adjustment  of  the  balance  and  this  tube 
were  such  that  the  rod  swung  freely,  and 
even  with  considerable  vibration  on  the 
lower  end  would  not  touch  the  sides  of 
the  tube. 

The  same  conditions  affecting  the  open- 

FIG.  46-— Weighing  Apparatus  for  Ob- 

mg  through  the  food  aperture  as  regards      jects  inside  the  chamber, 
necessity  for  preventing  leakage  of  heat 
or  air  obtained  in  making  this  opening 
through  the  calorimeter  chamber.     The 
leakage  of  heat  was  prevented  by  using 


A  chair  is 
suspended  on  a  rod  extending  from 
top  of  calorimeter  chamber.  A  metal 
yoke  is  hung  over  the  platform  of  bal- 
ance, so  that  chair  and  subject  can 
be  weighed  directly.  A  rubber  dia- 
phragm prevents  escape  of  air. 


160  A    RESPIRATION    CALORIMETER. 

the  fiber  tube,  which  is  an  excellent  non-conductor  of  heat.  To  pre- 
vent the  leakage  of  air,  we  at  first  used  a  thin  rubber  balloon  with  a 
small  opening  in  one  end  so  that  the  rod  could  pass  through  it,  the 
balloon  being  tightly  tied  to  the  rod  and  attached  to  the  tube.  It  was 
thus  possible  to  provide  for  not  only  the  necessary  up-and-down  motion, 
but  also  a  slight  lateral  motion  which  would  accompany  the  weighing 
and  at  the  same  time  prevent  any  loss  of  air  from  the  system.  Later, 
thin- walled  rubber  tubing  of  large  diameter  was  substituted.  This  thin 
rubber  diaphragm  prevents  the  escape  of  air  ;  but  it  is  necessary  to  rely 
on  this  closure  only  during  the  actual  period  in  which  the  weighings 
are  being  made,  since  the  flexibility  of  the  diaphragm  is  such  as  to  allow 
the  rubber  stopper  on  the  lower  end  of  the  suspension  rod  to  be  raised 
about  1.5  cm.,  which  is  sufficient  to  crowd  it  well  into  the  open  end  of 
the  fiber  tube,  thus  completely  shutting  off  the  tube  from  the  calorimeter 
chamber  proper. 

The  rubber  diaphragm  is  so  light  that  the  slight  vertical  motion  pro- 
duces no  variation  in  weight.  The  extreme  sensitiveness  of  the  platform 
balance  under  these  conditions  makes  it  possible  to  read  not  only  the 
graduations  on  the  scale-beam,  which  are  made  in  ic-gram  divisions,  but 
also  the  differences  in  height  at  the  end  of  the  scale-beam  itself.  A 
small  metal  pointer  is  attached  to  the  end  of  the  scale-arm  and  a  milli- 
meter scale  is  placed  immediately  behind  it  in  such  a  manner  that,  during 
the  progress  of  weighing,  the  pointer  moves  over  the  millimeter  scale. 
A  certain  arbitrary  point  is  taken  on  this  scale  as  the  zero  point.  The 
finer  weighings  are  made  by  means  of  a  second  hanger,  which  is  very 
much  smaller,  consisting  practically  of  a  stout  piece  of  copper  wire, 
which  is  of  such  a  weight  that  moving  it  through  a  section  of  the  grad- 
uated beam  corresponding  to  200  grams  is  equivalent  to  an  alteration 
in  weight  of  5  grams ;  and  it  was  found  that  by  its  use,  even  with  a 
weight  of  90  kg.  suspended  from  the  platform  balance,  weighings  to 
within  2  grams  or  even  i  gram  could  be  accurately  made. 

In  using  this  balance  it  is  necessary  only  to  obtain  actual  differences 
in  weight,  and  hence  no  correction  is  made  for  the  added  weight  of  the 
pointer  on  the  scale-arm,  the  removal  of  the  hooks  from  the  platform 
balance  itself,  the  weight  of  the  hanger  and  suspension  rod,  or  of  the 
stopper  and  ring  at  the  lower  end.  The  actual  weight  of  the  man  can 
be  obtained,  however,  since  two  series  of  weighings  are  made,  one  in 
which  the  man,  bedding,  clothing,  etc.,  are  weighed  with  the  man  sitting 
in  the  chair,  and  one  in  which  only  the  chair  plus  bedding  and  clothes 
are  weighed.  The  difference  between  these  two  weights  obviously  gives 
the  weight  of  the  man  himself. 


THE    CALORIMETER   SYSTEM   AND   MEASUREMENT   OF  HEAT.       l6l 

To  support  the  man  in  a  comfortable  position  while  being  weighed, 
we  have  provided  a  chair  which  can  be  suspended  from  the  rod  of  the 
weighing  apparatus.  A  hard-wood  folding-chair,  which  has  been  in 
use  regularly  inside  the  chamber  for  a  number  of  years,  was  utilized 
for  this  purpose.  This  is  shown  in  figure  46. 

A  chain  (or  at  present  a  phosphor-bronze  tiller  rope)  is  fastened  to 
the  back  of  the  chair  and  to  the  legs  in  such  a  manner  that  it  can  be 
suspended.  To  spread  the  rope  at  the  front  end  of  the  chair  seat,  two 
oak  blocks  through  which  the  rope  passes  were  hinged  under  the  seat. 
.  A  piece  of  gas-pipe  with  a  hook  serves  to  suspend  the  chair  and  act  as 
a  spreader  at  the  top.  By  using  this  spreader  arm  more  space  is  given 
between  the  chains  for  the  arms  and  shoulders  of  the  subject.  The 
chair  is  hooked  into  the  spreader  arm  in  such  a  position  that  during  the 
weighing  the  subject  faces  the  window. 

The  upper  end  of  the  suspension  rod  for  the  weighing  system  passes 
through  a  hole  in  the  hanger  on  the  platform  balance.  Two  nuts  are 
screwed  on  the  end  of  the  rod,  the  upper  one  of  which  serves  as  a  lock- 
nut.  It  is  thus  possible  to  raise  or  lower  the  rod  by  adjusting  these  two 
nuts.  The  rod  is  so  adjusted  that  when  the  rubber  stopper  is  removed 
from  the  fiber  tube  it  swings  perfectly  free,  and  there  is  no  danger  of 
touching  the  side  of  the  fiber  tube.  When  the  stopper  is  put  in  place, 
the  suspension  rod  slips  freely  up  through  the  hole  in  the  hanger,  and 
the  friction  of  the  rubber  stopper  in  the  fiber  tube  holds  the  rod  up  in 
place.  It  has  been  found  by  experience  that  the  taper  on  the  stopper 
is  such  that  it  can  be  inserted  in  the  fiber  tube  and  support  the  rod 
above  it  without  any  danger  of  slipping  out.  When  not  in  actual  use 
for  weighing,  the  stopper  is  always  crowded  well  into  place. 

On  the  end  of  the  suspension  rod  there  is  simply  a  large  iron  ring, 
and  it  was  found  inconvenient  to  suspend  everything  from  this  ring 
without  any  intervening  adjustment ;  consequently  a  hanger  consisting 
of  a  regular  gas-fitter's  cross  was  attached.  Into  opposite  sides  of  two 
of  the  openings  in  the  cross  two  half -inch  pipes  (16  mm.  internal  diam- 
eter) are  screwed.  These  pipes  are  14  cm.  long,  are  open  at  the  end, 
and  have  a  7  mm.  hole  drilled  on  the  under  side  8  mm.  from  the  open 
end.  A  stout  iron  hook  is  screwed  into  a  hole  drilled  in  the  side  of  the 
cross,  and  can  be  inserted  in  the  ring  on  the  end  of  the  suspension  rod. 
When  suspended  in  this  way,  the  cross  lies  parallel  to  the  top  of  the 
chamber.  In  the  other  two  arms  of  the  cross,  reducers  and  smaller 
pipes  1 8  cm.  long  and  10  mm.  internal  diameter  are  screwed  and  are 
used  for  suspending  the  absorbing  system. 

Weighing  the  absorbing  system. — In  weighing  the  absorbing  system  as 
was  formerly  done  by  the  use  of  spring  balances,  the  accuracy  was  not 

I  IB 


1 62  A    RESPIRATION   CALORIMETER. 

at  all  comparable  with  the  precision  obtainable  in  weighing  with  the 
system  just  described.  Arrangements  were  accordingly  devised  so  that 
the  absorbers  could  be  weighed  by  this  system. 

The  bulk  of  the  weight  of  the  absorbing  system  is  borne  by  three 
equipoises,  one  of  which  is  shown  in  figure  33.  These  three  points  of 
support  prevent  any  great  lateral  motion  of  the  system.  The  system 
is  suspended  by  attaching  eighth-inch  iron  pipe  (3  mm.  internal  diam- 
ter)  to  the  pipes  in  the  hanger  and  thence  to  the  absorbing  system.  A 
piece  of  stout  copper  wire  was  wound  about  the  upper  coil  of  pipe  in 
the  absorbing  system  at  the  rear  of  the  chamber  so  as  to  form  a 
loop.  The  3  mm.  pipe  was  slipped  through  one  end  of  this  loop  and 
the  other  end  into  the  pipe  of  the  hanger.  Two  similar  loops  of  stout 
copper  wire  were  attached  to  the  absorbing  system  near  the  front  on 
both  sides  about  42  cm.  from  the  corner.  A  long  T  was  then  made  of 
three  pieces  of  the  3  mm.  pipe,  the  two  arms  of  theT  were  slipped  through 
these  copper  loops,  and  the  stem  of  the  T  inserted  in  the  pipe  in  one  arm 
of  the  cross  or  hanger.  When  the  shields  were  lowered  to  such  a  point 
that  their  weight  rested  on  the  copper  disks,  the  lead  counterpoises  were 
raised  from  their  position  and  the  whole  system  became  suspended  on 
the  central  suspension  rod  of  the  weighing  system.  Owing  to  varia- 
tions in  the  amount  of  water  condensed  on  the  surface  of  the  different 
portions  of  the  absorbing  system,  it  became  necessary  to  balance  the 
system  in  such  a  manner  that  the  three  lead  counterpoises  and  equal 
beams  should  be  in  an  approximately  level  position  and  clear  of  the 
absorbing  system.  This  balancing  was  done  by  shifting  two  lead  weights 
provided  with  hooks  in  the  top,  which  could  be  hung  on  the  3  mm.  pipe 
used  to  support  the  absorbing  system.  After  a  little  practice  the  subject 
could  slide  the  weights  along  these  pipes  and  bring  the  whole  system 
into  equilibrium  very  rapidly.  When  in  equilibrium  an  observer  out- 
side signaled  the  assistants  stationed  at  the  balance  overhead  and  the 
weighing  was  made. 

Owing  to  the  multiplicity  of  bearings  of  the  three  equipoises,  the 
degree  of  accuracy  obtained  when  weighing  the  man  was  not  to  be  ex- 
pected. It  was  found,  however,  that  when  the  adjustments  were  prop- 
erly made,  differences  in  weight  of  the  absorbing  system  of  i  or  2  grams 
could  be  accurately  determined.  Thus  we  have  a  method  for  noting 
changes  in  weight  of  the  absorbing  system  that  is  as  accurate  as  could 
be  desired,  for  it  is  more  than  probable  that  the  amount  of  moisture 
condensed  on  the  surface  of  the  calorimeter,  the  bicycle  ergometer,  the 
telephone,  connecting  wires,  etc.,  sometimes  amounts  to  i  or  2  grams, 
and  hence  weighings  closer  than  this  would  have  no  significance. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT   OP   HEAT.       163 

Before  weighing  the  absorbing  system,  it  is  necessary  that  the  subject 
draw  off  all  drip  water  that  can  be  removed  from  the  cans  at  the  corners 
of  the  absorbing  system.  It  is  absolutely  essential  that  no  considerable 
amount  of  water  remains  in  the  aluminum  shield.  It  occasionally 
happens  that  the  outlet  pipe  from  the  shield  becomes  clogged  with  dirt 
or  dust,  and  the  drip  water,  instead  of  running  directly  into  the  cans, 
accumulates  in  the  shield  itself.  Under  these  conditions,  when  the 
subject  attempts  to  adjust  the  absorbing  system  for  weighing,  the  water 
will  flow  back  and  forth  from  one  end  of  the  absorber  to  the  other  end 
and  thus  produce  a  constantly  changing  weight  that  can  not  be  properly 
estimated. 

After  the  weighing  is  completed,  the  observer  outside  raises  the  lever- 
arm  until  the  flexible  cable  begins  to  raise  the  shields,  thus  removing  a 
portion  of  the  weight  of  the  absorbing  system.  The  lead  counterpoises 
then  settle  into  position  and  the  subject  can  remove  the  pipes  used  to 
suspend  the  absorbing  system.  After  removing  the  cross,  the  rubber 
stopper  can  be  re-inserted  in  the  fiber  tube. 

Routine  of  the  weighings. — Since  the  experimental  day  begins  at  7 
o'clock  in  the  morning,  it  is  desirable  to  have  the  weight  of  the  sub- 
ject, bedding,  and  furniture  at  this  hour  every  day  ;  consequently  the 
following  routine  was  utilized  in  the  later  experiments  of  1904  :  The 
subject  was  called  at  7  a.  m.  He  immediately  rose,  and,  having  slept  in 
underclothing  and  socks,  no  change  in  clothing  was  made.  He  then 
rolled  up  the  bedding,  fastened  the  bed  to  the  side  of  the  wall,  sus- 
pended the  chair  in  which  he  was  to  be  weighed  from  the  iron  hook  in 
the  end  of  the  suspension  rod,  and,  taking  all  the  bedding  and  clothing 
in  his  lap,  sat  in  the  chair.  By  means  of  a  speaking  tube  and  an  electric 
bell  connected  with  the  closet  upstairs  in  which  the  balance  is  placed,  a 
signal  was  given,  whereupon  two  observers  upstairs  brought  the  balance 
to  equilibrium  and  the  actual  weight  was  recorded  by  both.  The  subject 
was  then  signaled  to  get  up  from  the  chair,  and  he  immediately  placed 
all  the  clothing  (save  that  which  he  was  actually  wearing)  and  the 
bedding  in  the  chair.  This  weighing  was  made,  followed  by  the  adjust- 
ment and  weighing  of  the  absorbing  system. 

It  is  thus  seen  that  the  most  rapidly  fluctuating  weight,  i.  e.,  the 
weight  of  the  man,  was  made  first,  almost  immediately  after  7  o'clock. 
The  weight  next  most  liable  to  fluctuate,  i.  e.,  that  of  the  bedding  and 
of  the  clothing,  was  made  a  few  moments  later,  and  the  absorbing  system, 
which  it  is  supposed  would  fluctuate  in  weight  the  least,  especially  at 
this  hour  of  the  day,  was  not  weighed  until  the  last. 

The  necessity  for  weighing  the  man  as  soon  as  possible  after  7  o'clock 
is  seen  when  it  is  considered  that  there  is  a  loss  in  respiration  and  per- 


164  A   RESPIRATION   CALORIMETER. 

spiration  amounting  to  not  far  from  i  to  2  grams  per  minute,  and  hence 
it  was  our  effort  to  have  the  weight  of  the  man  recorded  at  exactly  the 
same  moment  after  7  o'clock.  Theoretically,  inasmuch  as  the  quantities 
of  carbon  dioxide  and  water  vapor  in  the  air  are  determined  precisely 
at  7  o'clock,  the  three  weighings  should  be  made  at  exactly  this  hour  ; 
but,  as  a  matter  of  fact,  this  was  distinctly  impracticable,  and  we  believe 
that  the  routine  here  employed  gives  results  that  are  not  far  from 
correct.  With  a  subject  who  had  never  been  inside  the  chamber  before, 
this  routine  of  weighing  man,  then  chair  plus  bedding,  then  absorbing 
system,  took  not  far  from  10  to  12  minutes  each  morning. 

Checks  on  the  accuracy. — This  method  of  weighing  was  very  carefully 
checked  by  weighing  the  subject  in  the  chair  and  then  placing  several 
brass  weights  in  his  lap.  It  was  found  that,  allowing  for  the  slight  loss 
from  perspiration  and  respiration,  the  gain  noted  by  the  observers  on 
the  platform  balance  above  corresponded  exactly  to  the  weights  added. 
The  accuracy  of  the  weighing  of  the  absorbing  system  was  determined 
in  a  similar  way.  A  small  wire  basket  was  constructed  so  as  to  hang 
directly  from  the  hanger  itself  or  in  any  position  on  the  trough,  and 
thus  correspond  to  varying  quantities  of  moisture.  By  placing  weights 
in  the  basket  in  different  positions,  the  accuracy  and  sensitiveness  of 
the  whole  system  could  thus  be  easily  tested.  Frequently  weights 
were  placed  on  the  lead  counterpoises,  and  the  apparent  loss  of  weight 
of  the  system,  as  detected  on  the  platform  balance,  always  agreed  very 
satisfactorily  with  the  weights  thus  added. 

It  seems  fair  to  assert,  therefore,  that  it  is  possible  to  weigh  a  man,, 
his  bedding  and  clothing,  and  the  absorbing  system  to  within  5  grams, 
if  not  less,  and  thus  the  weighing  of  these  objects  is  now  sufficiently 
accurate  to  serve  as  a  check  on  the  oxygen  determinations.  Indeed,  it 
is  not  impossible  that  the  indirect  determination  of  oxygen  by  this  means 
may  ultimately  take  the  place  of  the  direct  method  now  employed. 

THE  ERGOMETER. 

Many  problems  in  metabolism  require  for  proper  study  a  knowledge 
of  the  external  muscular  work  performed  by  the  body.  The  utilization 
of  the  various  nutrients  as  sources  of  muscular  energy,  the  isodynamic 
replacement  of  the  nutrients  in  diets  for  muscular  work,  and  the 
efficiency  of  the  body  as  a  machine  may  be  mentioned  as  among  the 
problems  of  this  nature.  Considerable  attention  has  therefore  been 
devoted  by  investigators  to  securing  an  accurate  measurement  of  external 
muscular  work. 

The  first  method  used  in  connection  with  the  experiments  with  the 
respiration  calorimeter  consisted  of  raising  and  lowering  a  weight  by 


To  face  page  164. 


FIG.  47. — The  Bicycle  Ergometer.  The  rear  wheel  of  a  bicycle  is  replaced  by  a  copper  disk  which 
can  be  rotated  iu  the  field  of  a  magnet.  The  strength  of  the  magnet  can  be  varied  by  the  quan- 
tity of  electricity  passing  through  the  field  coils.  The  principle  is  that  of  the  electric  brake. 


Kio.  48. — The  Electric  Counter.  An  armature  which  is  attracted  by  two  magnets  is  caused  to 
actuate  the  ratchet  on  a  revolution  counter.  The  instrument  is  connected  electrically  with  the 
bicycle  ergometer. 


THE   CALORIMETER   SYSTEM   ?  ND   MEASUREMENT   OF   HEAT.       165 

means  of  a  cord  over  a  pulley,  though  the  still  cruder  means  of  filing  a 
given  weight  of  iron  filings  from  a  piece  of  cast  iron  was  used  in  one 
of  the  preliminary  experiments.  In  both  of  these  methods  obviously 
but  very  crude  estimates  as  to  the  actual  amount  of  external  muscular 
work  performed  could  be  made.  As  measures  of  relative  rather  than 
absolute  amounts,  they  were  less  objectionable,  but  at  best  they  were 
far  from  the  accuracy  that  has  been  striven  for  in  the  development  of 
the  respiration  calorimeter  and  its  accessory  apparatus. 

It  was  observed  that  the  greatest  amount  of  work,  with  the  minimum 
fatigue,  could  be  performed  on  a  bicycle,  and  accordingly  an  ergometer 
was  constructed  in  which  a  pulley  attached  to  the  armature  shaft  of  a 
small  dynamo  was  braced  against  the  rear  tire  of  a  bicycle  wheel. '  This 
instrument  could  be  calibrated  but  roughly,  to  be  sure,  but  did,  how- 
ever, serve  its  purpose  in  the  transitional  period  during  which  the 
bicycle  ergometer  described  beyond  was  in  process  of  development. 

Retaining  the  bicycle  form  so  that  the  bulk  of  the  work  is  done  by 
the  powerful  leg  muscles,  the  present  ergometer  consists  of  an  arrange- 
ment for  rotating  a  heavy  copper  disk,  corresponding  to  the  rear  wheel 
of  a  bicycle,  in  the  field  of  an  electro-magnet,  which  thus  gives  the  effect 
of  an  electric  brake.  The  apparatus  is  shown  connected  ready  for  use 
in  figure  47. 

The  principle  is  the  well-known  one  of  magnetic  induction.  A  current 
of  electricity  is  passed  through  the  field  coils  of  the  magnet,  and  when 
power  is  applied  to  the  pedals  of  the  wheel  and  transmitted  to  the  revolv- 
ing disk,  it  is  transformed  into  heat.  To  calibrate  the  apparatus,  it  is 
put  inside  the  respiration  chamber  in  such  a  way  that  the  axle  of  the 
wheel  is  connected  to  a  shaft  which  passes  through  the  food  aperture 
and  is  revolved  by  power  applied  outside.  The  rate  of  revolution  is 
shown  by  a  cyclometer.  The  strength  of  the  magnet  is  determined  by 
the  electric  current  through  the  coils,  which  is  measured.  With  a  given 
strength  of  magnetization  the  power  applied  to  the  pedals  and  conse- 
quent heat  generated  will  vary  directly  as  the  speed  of  revolution  ;  the 
heat  is  therefore  measured  for  different  rates  of  speed.  The  data  thus 
obtained  show  the  amounts  of  energy  transformed  per  revolution  with 
the  given  magnetization.  The  mechanical  friction  in  the  ergometer  per 
revolution  is  constant  and  included  in  the  calibration.  Accordingly, 
when  the  man  is  working  on  the  ergometer,  the  number  of  revolutions 
as  recorded  by  a  cyclometer  multiplied  by  the  energy  per  revolution 
gives  the  muscular  work  done  at  the  pedals.  We  believe  the  measure- 
ments are  accurate  within  a  fraction  of  I  per  cent.  The  apparatus 
has  proved  very  satisfactory. 

aU.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  136,  p.  31. 


166  A   RESPIRATION    CALORIMETER. 

The  number  of  revolutions  of  the  pedal  of  the  ergometer  is  recorded 
on  the  observer's  table  by  the  cyclometer  shown  in  figure  48,  which  is 
designated  as  the  Dinsmore  electric  counter,  since  it  was  devised  by  our 
mechanician,  Mr.  Dinsmore. 

This  instrument  consists  of  an  electro-magnet  and  armature,  the 
latter  having  a  projection  which  extends  to  the  ratchet  wheel  of  the 
cyclometer.  A  device  on  the  crank  wheel  of  the  ergometer  closes  a 
circuit  to  the  magnet  at  each  revolution,  and  thus  actuates  the  armature. 

Correction  for  the  magnetization  of  the  fields  of  the  ergometer. — In  work 
experiments  with  the  ergometer  a  correction  of  the  heat  measured  by 
the  calorimeter  is  necessary  because  of  the  heat  added  to  the  chamber 
in  magnetizing  the  fields  of  the  ergometer.  The  amount  of  heat  thus 
added  varies  with  the  strength  of  current.1  For  the  strength  generally 
employed,  namely,  1.25  amperes,  it  amounts  to  10.94  large  calories  per 
hour,  which  is  accordingly  deducted  from  the  heat  measured. 

BLANKS  USED  FOR  HEAT  RECORDS. 

A  specimen  page  from  the  calorimetric  records,  showing  the  printed 
blank  in  use  in  the  heat  calculations,  with  observations  for  a  portion  of 
an  actual  experiment  recorded  therein,  is  given  on  page  167.  For  a 
clear  understanding  of  this  sheet,  reference  to  figure  43  is  also  necessary. 

It  will  be  noted  that  at  the  top  of  the  sheet  are  recorded  the  date,  the 
number  of  the  experiment,  and  the  name  of  the  observer.  Then  follow 
ten  vertical  columns,  in  which  are  inserted  the  various  readings  for  one 
hour.  A  space  at  the  bottom  of  the  sheet  allows  for  further  observa- 
tions if  necessary. 

In  the  first  vertical  column  is  inserted  the  time  of  each  reading.  It 
is  so  arranged  that  these  may  be  recorded  every  two  minutes,  though  as 
a  matter  of  fact  it  has  been  found  that  in  ordinary  rest  experiments 
four-minute  readings  are  sufficient,  except  at  periods  of  increased  bodily 
activity,  as  at  7  a.  m.,  when  the  subject  is  dressing  and  carrying  out 
the  somewhat  extensive  routine  elsewhere  outlined.  At  such  times 
certain  readings  are  recorded  every  two  minutes  as  long  as  vigorous 
activity  continues. 

The  second  column  is  headed  "  Inner  walls,  No.  i."  In  this  are 
recorded  the  deflections  produced  by  pressing  down  the  key  marked 
A  Iy  I,  No.  i,  in  figure  43.  The  third  column  gives  similar  readings 
for  the  incoming  air  current,  as  shown  by  key  No.  2,  and  the  fourth 
the  deflections  for  the  outer  walls,  as  indicated  by  the  key  marked 
A  Iy  L  No.  3.  The  readings  obtained  from  these  three  keys  are  recorded, 

1  The  calculation  is  made  according  to  the  formula  C  X  E  X  I  X  0.2385  =  calories. 
See  page  172. 


THE   CALORIMETER   SYSTEM   AND   MEASUREMENT   OF   HEAT.       167 
Metabolism  Experiment  No.  70.    H.  C.  Martin,  Observer. 


Date,  December  20,  1904. 


Time, 
(a.m.) 

Inner 

walls. 
No.  i. 

1 

Moving 
air. 
No.  2. 

-          + 

Outer 

wall. 
No.  3. 
—        + 

Inside 
temp. 
No.  5. 

Temp, 
water 
therm. 

Cor- 
rected 
temp. 

Dif- 
fer- 
ence. 

Heat  calculations. 
No.  7.      T         B 

Sundries. 
R          8=120. 

&% 

% 

14-24 

14.18 

10.00 

2 

^ 

i 

106^ 

10.39 

10.38 

3-8o 

60         20.3      20.84 

3>J4 

02 

14.26 

14.20 

04 

5 

i^ 

% 

108 

10.29 

10.28 

3-92 

61 

31%  Sits  up  and 

drinks. 

06 

68.4  at  10:08:42 

14.29 

14-23 

OS 

&% 

% 

5 

H3 

10.24 

10.23 

4.00 

63  45.25  at  4.114 

31^  Liesdown; 

reads. 

10 

10.050  K. 

14-32 

14.26 

12 

1% 

X 

13 

116 

10.16 

10.15 

4.11 

66 

3i/4    41-35  calo- 

ries. 

11 

I4-5I 

14-45 

16 

4 

I 

i% 

H5 

10.16 

10.15 

4-30 

66% 

yM 

18 

14.58 

14-52 

30 

3% 

1^ 

i% 

114 

10.12 

10.  II 

4.41 

66 

3oH 

22 

14.60 

14-54 

24 

1% 

IM 

i% 

«aM 

IO.O4 

10.03 

4-5i 

65 

3i 

26 

14.58 

14-52 

28 

i* 

1% 

3% 

in% 

10.23 

10.22 

4-30 

64% 

31* 

30 

Telephones. 

14-59 

14-53 

32 

% 

% 

6% 

1  10^ 

10.20 

10.19 

4-34 

63% 

31  y2  Sits  up  and 

31 

19.8      20.87 

opens  food 
aperture. 

14.68 

14.62 

36 

6 

3% 

i% 

"7M 

IO.I4 

10.13 

4-49 

67 

32j* 

38 

Lies   down 

14.87 

I4.8I 

and  reads. 

40 

2 

% 

13 

»7M 

10.14 

10.13 

4.68 

68 

335* 

42 

14-99 

14-93 

44 

6 

3 

7 

»3J* 

IO.2I 

10.  2O 

4-73 

67* 

33% 

46 

15-01 

M.95 

48 

1% 

2 

5^ 

in 

IO.26 

10.25 

4.70 

65 

33% 

60 

79.8  at  10:52:38 

14.76 

14.70 

52 

i* 

I 

5% 

noM 

10.26 

10.25 

4-45 

64^  49.02  at  4.456 

33% 

54 

10.102  K. 

45.01  calo- 

14-57 

14.51 

ries. 

56 

iM 

2* 

*% 

no 

10.32 

10.31 

4.20 

63 

34  J* 

58 

27^  29^ 

I2}6      lOji 

REMARKS  : 


1 68  A   RESPIRATION   CALORIMETER. 

if  positive,  on  the  right-hand  side  of  their  respective  columns,  under  the 
sign  +,  and  if  negative,  on  the  left-hand  side,  under  the  sign  — .  As 
has  been  explained,  the  deflections  should  with  each  key  be  as  near 
zero  as  possible.  This  is  especially  necessary  with  Nos.  i  and  2.  At  the 
end  of  each  hour  the  sum  of  the  readings  in  each  of  these  columns  is 
taken,  and  the  difference  between  the  sums  carried  over  to  the  following 
sheet,  to  be  compensated  for  if  possible  during  the  next  hour. 

The  fifth  column  is  headed  "Inside  temp.,  No.  5."  In  this  are 
recorded  the  deflections  with  key  No.  5,  which  represent  the  temper- 
ature just  inside  the  copper  walls  as  measured  by  the  electrical  ther- 
mometer described  on  page  135.  This  temperature  is  held  as  nearly 
uniform  as  practicable. 

The  three  columns  following  are  used  for  recording  the  temperature 
of  the  incoming  and  outgoing  water  current.  That  headed  ' '  Temp, 
water  therm. ' '  gives  the  readings  of  the  mercurial  thermometers,  that  in 
the  outgoing  water  current  being  recorded  above  with  the  correspond- 
ing reading  of  the  incoming  water  current  immediately  below.  In  the 
next  column  are  the  readings  as  corrected  for  the  calibrations  of  the 
thermometers  (see  p.  133).  The  column  headed  ' '  Difference  ' '  contains 
the  differences  between  the  corrected  readings  for  the  incoming  and 
outgoing  water  current,  or,  in  other  words,  the  rise  in  temperature  of 
the  water  current. 

In  the  column  headed  "  Heat  calculations  "  are  recorded  various  mis- 
cellaneous data.  The  left-hand  margin  contains  the  readings  with 
key  No.  7,  the  electrical  thermometer  connected  with  the  copper  walls 
and  showing  their  temperature.  Readings  of  T,  the  mercurial  ther- 
mometer just  outside  the  window,  and  of  B,  the  mercurial  thermometer 
inside  (see  p.  120),  are  also  taken  from  time  to  time  and  recorded  in 
this  column.  Whenever  one  of  the  cans  on  the  water-meter  is  full,  the 
reading  of  the  dial,  together  with  the  time,  expressed  in  hours,  minutes, 
and  seconds,  is  recorded  ;  for  example,  79.8  at  10  o'clock  52  minutes 
38  seconds.  Just  below  this  is  written  the  sum  of  all  temperature  dif- 
ferences while  the  can  was  filling.  This  sum  divided  by  the  number 
of  readings  gives  the  average  rise  in  temperature  of  the  water  in  the 
can.  For  example,  the  sum  of  n  readings  was  49.02,  the  average  of 
which  was  4.456.  This  value,  multiplied  by  the  weight  of  the  water 
as  determined  from  a  plotted  curve  for  the  point  corresponding  to  the 
figure  registered  by  the  dial  (see  p.  132),  gives  the  heat  in  calories 
brought  out  from  the  calorimeter  system  for  the  period  of  time.  This 
value  is  recorded  in  the  last  column  (45.01  calories). 

The  final  column,  marked  "Sundries,"  also  serves  for  miscel- 
laneous data.  When  the  rectal  thermometer  is  in  use,  its  readings 


TESTS   OF   ACCURACY   OF  HEAT-MEASURING   APPARATUS.         169 

are  here  recorded  under  the  designation  R.  Occasional  readings  of  S, 
giving  normal  or  standard  deflections  of  the  galvanometer,  are  here 
given,  and  any  additional  observations  of  the  assistant,  particularly  as 
to  the  movements  of  the  subject,  are  here  briefly  stated. 

The  heat  sheet  therefore  serves  as  a  source  of  original  data  regarding 
the  gain  or  loss  of  heat  through  the  walls,  the  maintenance  of  constant 
temperature,  the  estimation  of  the  heat  brought  away  by  the  water  cur- 
rent, the  body  temperature,  and  the  more  important  movements  of  the 
subject. 


TESTS  OF  THE  ACCURACY  OF  THE  HEAT-MEASURING  APPARATUS. 

For  testing  the  accuracy  of  the  calorimetric  features  of  the  apparatus 
two  special  forms  of  test  have  been  devised.  In  one  a  definite  amount 
of  heat  is  generated  inside  the  chamber  by  means  of  the  passage  of  an 
electric  current  through  a  known  resistance.  Knowing  the  strength  of 
current  and  the  fall  of  potential,  it  is  possible  to  calculate  accurately 
the  quantity  of  heat  thus  developed  and  compare  it  with  that  brought 
away  by  the  water  current.  These  tests  are  called  electrical  check 
experiments. 

A  second  test  is  obtained  by  burning  known  weights  of  ethyl  alcohol 
inside  the  calorimeter  and  measuring  the  energy  thus  produced.  From 
the  weight  of  the  alcohol  and  the  heat  of  combustion  as  determined  by 
the  bomb  calorimeter  it  is  possible  to  compute  the  amount  of  heat  which 
theoretically  should  be  developed  and  compare  it  with  that  brought 
away  by  the  water  current.  These  are  called  alcohol  check  tests. 

ELECTRICAL   CHECK  TESTS. 

The  development  of  a  known  amount  of  heat  by  means  of  the  electric 
current  necessitates  an  accurate  knowledge  of  four  factors  :  First,  the 
strength  of  current;  second,  the  fall  of  potential;  third,  the  time  in 
seconds,  and  fourth,  the  factor  for  the  conversion  of  electric  units 
to  that  of  heat.  Of  these  four  factors  we  have  to  consider  only  those 
of  the  strength  of  electric  current,  fall  of  potential,  and  the  conversion 
factor.  The  strength  of  the  current  in  these  experiments  was  deter- 
mined by  passing  it  through  a  milli-ammeter,  which  was  especially 
calibrated  for  us  by  the  Weston  Electrical  Instrument  Company,  of 
Newark,  New  Jersey,  and  guaranteed  by  them  to  give  readings  within 
o.  i  per  cent.  In  this  instrument  the  maximum  current  that  could  be 
measured  was  1.5  amperes.  The  instrument  has  been  compared  from 
time  to  time  with  a  Kelvin  balance  with  no  noticeable  variations  in 
accuracy. 


A   RESPIRATION   CALORIMETER. 

The  fall  in  potential  is  measured  by  an  accurate  voltmeter,  constructed 
by  the  same  company,  with  an  accuracy  guaranteed  to  be  within  o.  i 
per  cent.  The  maximum  voltage  that  can  be  read  on  this  instrument 
is  150.  The  accuracy  of  this  instrument  has  been  frequently  tested 
by  comparison  with  a  standard  Weston  voltmeter. 

The  electrical  connections  are  shown  diagrammatically  in  figure  49. 

The  present  arrangement  consists  of  a  loo-ohm  resistance  coil  of 
German-silver  wire  wound  on  a  wooden  frame  and  suspended  within 
the  chamber.  This  coil  is  capable  of  carrying  a  current  of  i .  5  amperes. 


FIG.  49. — Connections  for  Electrical  Check  Experiment.  An  electric  current  from  a  storage  bat- 
tery is  passed  through  the  ammeter  and  then  through  a  coil  hung  in  calorimeter  chamber. 
By  means  of  a  variable  resistance  the  strength  of  current  can  be  kept  constant.  A  voltmeter 
gives  the  fall  of  potential. 

Connections  are  made  with  the  milli-ammeter  on  one  side  and  with  a 
switch  connected  with  the  storage  battery  on  the  other  side.  The  milli- 
ammeter  is  also  connected  with  a  switch.  Two  wires  connect  the  volt- 
meter with  the  coil  inside  the  chamber,  and  thus  the  fall  of  potential  as 
the  current  passes  through  the  coil  is  accurately  measured.  The  current 
from  the  storage  battery  therefore  passes  in  series  through  the  milli- 
ammeter,  the  coil  inside  the  chamber,  and  then  through  a  variable  resist- 
ance back  to  the  switch.  By  varying  this  resistance,  the  strength  of 
current  passing  through  the  coil  can  be  adjusted  with  great  accuracy. 
Both  electrical  instruments  can  be  read  with  a  magnifying  glass  to  i 


TESTS  OF  ACCURACY   OF,  HEAT-MEASURING  APPARATUS.         171 

part  in  1,000.  A  sufficient  number  of  cells  of  storage  battery  are 
employed  to  give  a  strength  of  current  through  the  coil  of  about  i 
ampere  with  a  voltage  of  about  1 20. 

ELECTRICAL  UNIT  USED. 

In  the  fall  of  1904,  in  a  discussion  of  the  accuracy  of  the  bomb  calo- 
rimeter l  used  in  connection  with  these  experiments,  it  was  pointed  out 
by  Dr.  I,.  J.  Henderson,  of  Harvard  University,  that  the  heat  of  combus- 
tion of  standard  materials  such  as  naphthalene,  benzoic  acid,  and  cane 
sugar  were  noticeably  different  when  determined  by  the  bomb  calorimeter 
used  at  Wesleyan  University  and  when  determined  by  the  bomb  calo- 
rimeter used  by  Fischer  and  Wrede."  The  calorimeter  used  by  these 
writers  was  standardized  by  Jaeger  and  von  Steinwehr 3  by  an  electrical 
method  in  which  the  factor  0.2394  was  used  to  convert  watt-seconds  to 
calories. 

This  matter  was  referred  to  Dr.  E.  B.  Rosa,  formerly  professor  of 
physics  in  Wesleyan  University  and  at  present  physicist  of  the  National 
Bureau  of  Standards.  The  following  statements  are  essentially  those 
furnished  us  by  Dr.  Rosa. 

The  values  found  for  the  mechanical  equivalent  of  heat  by  the  elec- 
trical method  differ  appreciably  from  those  obtained  by  the  mechanical 
method.  There  is  reason  for  believing,  however,  that  the  values  of  the 
international  volt  and  ampere  are  about  o.  i  per  cent  too  large.  This 
is  a  subject  the  Bureau  of  Standards  and  others  are  now  investigating, 
but  absolute  measurements  for  determining  independently  the  volt 
and  ampere  are  difficult  to  make  and  the  question  is  not  yet  settled. 
Assuming  this  error  in  the  electrical  units,  the  values  of  J  deter- 
mined electrically  agree  very  well  with  Rowland's  value  determined 
mechanically,  and  this  is  the  best  value  yet  obtained  by  the  mechanical 
method. 

The  most  probable  value  for  J  (assuming  the  correction  of  o.  i  per 
cent  in  the  electrical  units)  is 

J=  4.181  x  io7  ergs,  at  20°. 

Allowing  for  the  variation  in  the  specific  heat  of  water,  the  heat 
required  to  raise  the  temperature  of  a  gram  of  water  i°  at  10°  would 
require  4.181  x  io7  x  1.0030  =  4.1935  X  io7  ergs. 

1  For  a  description  of  the  form  of  bomb  calorimeter  here  used  see  Jour.  Am.  Chem. 
Soc.  (1903),  25,  p.  659. 

'-1  Sitzungsber.  K.  Akad.  Wiss.  (1904),  pp.  687-715. 

3  Verhandlungen  ber.  deut.  phys.  Gesell.  (1903),  5,  2,  pp.  50-59. 


IJ2  A   RESPIRATION   CALORIMETER. 

The  energy  of  an  electric  current  is  CE/  X  IOT  ergs. ,  and  this  expressed 
in  calories  at  10°  is 

IE/  x  IQT_=  cE/x  0.23846  calories. 


4. 1935  X  10' 

But  this  is  on  the  assumption  that  our  electric  units  are  o.  i  per  cent 
too  small.  Since  we  are  using  these  same  small  units  in  our  work,  it  is 
evident  that  the  numerical  values  of  C  and  E  are  both  too  large  by  this 
amount,  and  therefore  the  product  too  large  by  o.  2  per  cent.  This  gives 
0.23846  —  0.00048  =  0.2380  as  the  true  conversion  factor. 

We  can  reach  the  same  result  by  taking  the  mean  of  the  results  for 
the  mechanical  equivalent  of  heat  obtained  by  Griffiths  (4. 192), Schuster 
and  Gannon  (4.189),  and  Callendar  and  Barnes  (4.186)  without  correc- 
tion for  the  supposed  error  in  the  electrical  units.  The  mean  of  these 
three  values  is  J  =  4. 189  X  io7  at  20°.  Correcting  this  to  10°,  we  have, 
multiplying  by  1.003  as  before,  J  =  4.2016  x  io7  at  10°.  Then 

CE/  X  io7  s  before> 


4-2OI6X  IO7 

Thus  no  account  need  be  taken  of  the  supposed  error  in  the  electrical 
units,  inasmuch  as  the  three  English  investigators  above  quoted  all  used 
substantially  the  same  electrical  units  that  are  now  used  in  Middletown. 
This  value  (0.2380)  is  slightly  different  from  that  used  earlier l  (0.2378), 
because  the  latter  is  based  on  Griffith's  value,  which  is  somewhat  larger 
than  the  mean  of  the  three  used  in  this  calculation. 

To  compare  this  with  the  value  given  by  Fischer  and  Wrede,  it  is 
necessary  to  reduce  to  15°  and  to  correct  for  the  difference  between  our 
electrical  units  and  those  used  in  Germany.  The  first  correction 
amounts  to  0.0019,  giving  0.2380  x  1.0019=  0.23845.  The  second 
amounts  to 

9/1 

=    0.0017. 


H340 

Thus  0.23845  x  1.0017  =  0.23885,  which  is  the  proper  value  at  15° 
to  use  in  Germany  ;  that  is,  with  German  electrical  units. 

A  value  as  large  as  o.  2394  can  not,  in  the  light  of  the  most  recent  work, 
be  justified. 

As  used  by  Jaeger  and  von  Steinwehr  it  was  apparently  taken  from 
the  values  given  by  Graetz.2 

1U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bull.  63,  p.  43. 
s  Winkelmann's  Handbuch  der  Physik,  2,  2,  p.  415. 


TESTS   OF   ACCURACY   OF   HEAT-MEASURING  APPARATUS.         173 

Graetz  quotes  the  results  obtained  by  Joule,  Rowland,  and  Miculescu. 
The  more  recent  investigations  of  Griffiths,  Schuster  and  Gannon,  and 
Callendar  and  Barnes  are  not  given.  Joule's  value  for  J  is  a  little  smaller 
than  Rowland's  and  the  recent  values  found  by  the  electrical  method. 
Graetz  takes  the  mean  of  the  three  values  quoted,  and  the  lower  value 
of  Joule's  result  makes  the  mean  a  little  lower,  namely,  4.177  x  io7  at 
15°.  The  reciprocal  of  this  is  o. 2394,  the  value  used  by  Jaeger  and  von 
Steinwehr  and  Fischer  and  Wrede. 

According  to  Dr.  Rosa,  the  best  principle  would  be  to  use  the  number 
0.2385  at  15°  and  then  correct  the  number  of  gram-degrees  measured  to 
calories  at  15°  by  multiplying  by  the  ratio  of  the  specific  heat  at  the 
given  temperature  to  that  at  15°. 

The  importance  of  the  electrical  unit  and  conversion  factor  in  connec- 
tion with  the  experiments  with  the  respiration  calorimeter  is  seen  when 
it  is  considered  that,  given  accurate  electrical  units  and  factors,  it  is 
possible  to  verify  the  bomb  calorimeter  by  the  respiration  calorimeter. 
By  burning  alcohol  in  the  bomb  calorimeter  a  certain  heat  of  combustion 
is  obtained,  and  if  the  alcohol  is  then  burned  in  the  respiration  chamber, 
which  has  been  calibrated  and  standardized  by  the  electrical  method, 
obviously  the  same  heat  of  combustion  determined  by  both  forms  of 
calorimeter  is  a  verification  of  the  bomb.1 

It  is  furthermore  significant  that  the  difference  between  the  heat  of 
combustion  of  cane  sugar,  naphthalene,  benzoic  acid,  and  other  standard 
materials,  when  determined  by  the  bomb  calorimeter  used  in  Middle- 
town  and  when  determined  by  Fischer  and  Wrede,  is  exactly  propor- 
tional to  the  difference  between  the  two  conversion  factors  used.  Pend- 
ing a  revision  of  the  electrical  units  by  the  National  Bureau  of  Standards, 
we  use  here  the  factor  0.2385  for  converting  watt-seconds  to  calories 
at  15°. 

LENGTH  AND  DURATION  OF  EXPERIMENTS. 

After  the  coil  and  connections  are  properly  installed  inside  the 
chamber  the  switch  is  closed,  and  the  water  current  passing  through 
the  heat-absorbers  is  regulated  so  that  the  heat  is  brought  away  at  the 
same  rate  at  which  it  is  generated.  After  an  hour  or  two,  during  which 
period  the  apparatus  comes  into  equilibrium,  the  experiment  proper  is 
begun.  The  experiment  lasts  usually  from  eight  to  twelve  hours,  during 
which  time  the  current  is  measured  by  the  milli-ammeter  and  is  kept 

1  For  a  discussion  of  the  verification  of  the  bomb  calorimeter  by  the  respiration 
calorimeter  see  Atwater  and  Snell,  Jour.  Am.  Chem.  Soc.  (i9°3).  25>  P-  698- 


174  A   RESPIRATION   CALORIMETER. 

constant  by  means  of  the  variable  resistance.  Readings  on  both  elec- 
trical instruments  are  taken  frequently  to  insure  complete  accuracy. 
At  the  end  of  the  period  the  time  in  seconds  is  noted  and  the  average 
reading  of  the  instrument  taken.  The  formula  for  computing  the 
amount  of  energy  developed  during  the  experiment  is  therefore 
C  X  E  X  /  X  o.  2385  —  calories,  in  which  C  is  the  strength  of  the  cur- 
rent in  amperes,  E  the  fall  of  potential  in  volts,  and  /  the  time  in 
seconds. 

RESULTS  OF  EI.ECTRICAI,  CHECK  EXPERIMENTS. 

The  last  electrical  check  experiment  made  with  the  apparatus  was  on 
November  22,  1904.  The  actual  period  of  measurement  extended  from 
i. 06  p.  m.  to  10.04  p.  m.,  or  8  hours  and  58  minutes.  During  this 
period  there  was  a  current  of  0.950  ampere  passed  through  the  coil  and 
a  fall  of  potential  of  99  volts.  By  using  the  formula  given  above,  the 
heat  generated  during  this  period  was  computed  to  be  723.7  calories. 
The  heat  measured  during  this  period  by  the  respiration  calorimeter 
was  721.73  calories,  or  99.72  per  cent  of  that  generated.  A  test  con- 
ducted a  month  before  gave  the  ratio  of  heat  measured  to  that  generated 
corresponding  to  99.59  per  cent.  It  thus  appears  that  the  apparatus 
measures  heat  developed  within  it  electrically  with  great  accuracy. 

THE    COMBUSTION    OP    ETHYL    ALCOHOL  AS   A   CHECK    ON    THE    HEAT 

MEASUREMENTS. 

Although  the  electrical  check  experiments  are  carried  out  with  great 
accuracy,  they  still  do  not  permit  of  the  testing  of  the  apparatus  under 
conditions  approximating  those  in  which  it  is  used  in  actual  experi- 
menting, and  obviously  the  question  of  the  heat  of  vaporization  of  water 
plays  no  r61e  in  the  electrical  check  experiment.  As  early  as  1779, 
Crawford l  endeavored  to  study  the  accuracy  of  the  heat  measurements 
of  his  calorimeter  by  burning  known  weights  of  charcoal,  lamp  oil,  wax, 
and  tallow  inside  the  chamber.  Subsequent  experimenters  have  used 
hydrogen,  stearin  candles,  ether,  and  other  substances.  As  a  result  of  a 
large  number  of  experiments  in  which  a  number  of  different  combustibles 
were  tried,  we  have  relied  upon  the  combustion  of  ethyl  alcohol  of  known 
water  content  for  this  purpose.  Inasmuch,  however,  as  the  combustion 
of  ethyl  alcohol  inside  the  chamber  results  not  only  in  an  evolution  of 
heat,  but  also  of  carbon  dioxide  and  water,  and  in  the  absorption  of 

1  Experiments  and  Observations  on  Animal  Heat  ;  see  also  Zeits.  f.  Biol.  (1894), 
30,  p.  76. 


TESTS   OF  ACCURACY   OF   HEAT-MEASURING   APPARATUS.         175 

oxygen,  the  combustion  of  alcohol  is  also  used  to  check  the  accuracy 
of  the  respiration  apparatus.  Such  experiments,  as  well  as  the  kind  of 
alcohol  used  and  determination  of  its  specific  gravity,  have  already  been 
considered  in  detail  (see  pp.  96-105). 

For  the  purpose  of  checking  the  apparatus  as  a  calorimeter,  a  knowl- 
edge of  the  heat  of  combustion  of  the  alcohol  used  is  essential. 

HEAT  OF  COMBUSTION  OF  ALCOHOL. 

For  the  determination  of  the  heat  of  combustion  we  resort  to  direct 
combustions  in  the  bomb  calorimeter.  A  large  number  of  such  com- 
bustions have  been  made  in  this  laboratory.  Since  absolute  alcohol 
absorbs  water  rapidly  from  the  air,  we  have  prepared  aqueous  solutions 
of  varying  degrees  of  strength  for  use  in  these  tests. 

A  known  weight  of  alcohol  is  placed  in  small  gelatin  capsules,  such 
as  are  used  frequently  for  the  administration  of  medicine.  When  gela- 
tin capsules  are  used  there  is  no  loss  by  volatilization,  and  as  the  heat 
of  combustion  of  the  gelatin  is  quite  constant  (about  4.452  calories  per 
gram)  the  absolute  amount  of  heat  introduced  with  the  alcohol  can  be 
determined  with  considerable  accuracy.  The  capsules  weigh  not  far 
from  0.3  gram,  thus  introducing  about  1.3  calories. 

Inasmuch  as  in  the  combustion  of  alcohol  a  certain  portion  of  the 
oxygen  combines  with  the  hydrogen  of  the  alcohol  to  form  water,  which 
is  condensed  inside  the  bomb,  the  gas  in  the  bomb  is  at  a  somewhat 
less  pressure  at  the  end  than  at  the  beginning  of  the  combustion.  The 
slight  expansion  of  the  residual  gas,  as  a  result  of  a  diminished  press- 
ure, produces  a  cooling  effect,  and  the  heat  of  combustion  of  the  alcohol 
must  be  corrected  for  constant  pressure.  It  is  necessary,  therefore,  to 
add  to  the  heat  of  combustion  of  the  alcohol  a  certain  factor  which  is 
obtained  in  the  following  manner :  To  reduce  the  molecular  heat  of 
combustion  of  a  solid  or  liquid,  the  formula  of  which  is  CnHpNrO(l,  from 
that  at  constant  volume  to  that  at  constant  pressure,  a  correction  would 
be  added  of  (%  p  —  q  —  r)T  calories,  where  T  equals  the  absolute  tem- 
perature of  the  calorimeter.1  To  reduce  the  specific  heat  of  combustion 
at  constant  volume  to  that  at  constant  pressure,  the  amount  to  be  added 
is,  therefore,  (%  p  —  q  —  r)  T  -=-  M,  where  M  equals  the  molecular  weight 
of  the  substance.  For  alcohol  this  correction  amounts  to  13  calories  per 
gram.  The  corrected  heat  of  combustion  of  anhydrous  ethyl  alcohol  is 
taken  in  this  discussion  as  7.080  calories  per  gram. 

1  For  discussion  of  this  point  see  Atwater  and  Snell,  Jour.  Am.  Chem.  Soc.,  25, 
I9°3,  PP-  690,  691. 


176 


A   RESPIRATION    CALORIMETER. 


RESULTS  OF  ALCOHOL  CHECK  EXPERIMENT. 

As  has  been  stated,  the  combustion  of  known  amounts  of  ethyl  alcohol 
inside  the  respiration  chamber  furnishes  the  means  for  verifying  the 
accuracy  not  only  of  these  portions  of  the  apparatus  which  have  to  do 
with  the  measurement  of  the  respiratory  products,  but  also  of  the  heat- 
measuring  features.  Consequently,  instead  of  discussing  the  check  on 
the  heat  determinations  as  a  separate  section,  a  summary  of  the  alcohol 
check  experiment  in  its  relation  to  the  determination  of  water,  carbon 
dioxide,  and  oxygen  as  given  on  pages  102-105  is  included  in  Table  4, 
with  the  data  on  the  determination  of  energy. 

TABLE  4. — Summary  of  Determinations  of  Water,  Carbon  Dioxide,  Oxygen,  and 

Energy. 

Alcohol  check  experiment,  April  6-7,  1905. 


Period. 

Duration. 

Alcohol 
burned. 

Water. 

Carbon  dioxide. 

Found. 

Required. 

Ratio. 

Found. 

Required. 

Ratio. 

First  

Mrs.  Mins. 
3       54 
5        441A 
ii        52 

Grams. 
73-4 
108.1 

225.3 

Grams. 

86.51 

124-33 
263.15 

Grams. 

84.98 
125.15 
260.83 

Percent. 
101.8 

99-3 
100.9 

Grams. 
126.70 
187.39 
392.10 

Grams. 
127.32 
18751 
390-81 

Per  cent. 
99-5 
99-9 
100.3 

Second  
Third  

21            30% 

406.8 

473-99 

470.96 

100.6 

706.19 

705.64 

IOO.I 

Period. 

Duration. 

Alcohol 
burued. 

Oxygen. 

Energy. 

Found. 

Required. 

Ratio. 

Found. 

Required. 

Ratio. 

First  

firs.  Mins. 
3       54 
5        44^ 
ii        52 

Grams. 

73-4 
108.1 

225.3 

Grams. 

139-35 
207.09 

431-09 

Grams. 

138.90 
204.56 

426.33 

Percent. 
1003 

IOI.2 
IOI.I 

Calories. 
417-86 
619.03 
1,292.97 

Caloriet. 
421.40 
620.61 
1,293-45 

Per  cent. 
99-2 
99-7 

IOO.O 

Second  
Third  

21          3<>M 

406.8 

777-53 

769.79 

IOI.O 

2,329.86 

2,335-46 

99.8 

This  experiment,  a  fair  sample  of  a  large  number  of  the  sort,  gives 
a  true  test  of  the  apparatus  in  all  its  phases.  The  determinations  of 
energy  are  as  satisfactory  as  could  be  expected,  averaging  99.8  per  cent 
of  the  required  amount.  The  summarized  results  for  the  determina- 
tion of  water,  carbon  dioxide,  and  oxygen  show  that  the  apparatus  is 
sufficiently  accurate  to  determine  these  three  factors  as  well  as  the 
energy  with  an  accuracy  approaching  that  of  the  most  approved  methods 
of  chemical  analysis. 


EXPERIMENT   WITH    MAN.  177 


EXPERIMENT  WITH  MAN. 

Obviously  with  an  apparatus  constructed  on  this  plan,  the  final  test 
of  its  practicability  lies  in  an  experiment  with  man.  Since  the  comple- 
tion of  the  new  apparatus,  22  experiments  with  5  different  subjects, 
covering  a  total  of  60  days,  have  been  conducted.  These  experiments 
lasted  from  i  to  13  days,  during  which  time  the  subject  remained 
inclosed  in  the  calorimeter  chamber.  Ordinarily  the  experiment  lasts 
3  or  4  days.  In  general,  each  experiment  is  preceded  by  a  preliminary 
period  outside  the  chamber,  during  which  the  subject  is  given  the  special 
diet  to  be  tested,  and  his  habits  of  life  so  modified  as  to  conform  with 
those  to  be  followed  in  the  chamber.  When  the  subject  is  to  be  engaged 
in  muscular  work,  he  devotes  considerable  time  in  the  preliminary  days 
to  riding  a  bicycle  in  the  open  air,  the  amount  of  work  performed  being 
as  nearly  as  can  be  judged  equivalent  to  that  to  be  done  later  on  the 
bicycle  ergometer  inside  the  chamber.  The  food  for  the  whole  experi- 
mental period,  including  the  preliminary  days,  is  carefully  weighed, 
sampled,  and  daily  portions  placed  in  proper  containers  ready  for  con- 
sumption. The  more  easily  decomposed  materials,  such  as  milk  and 
cream,  are  sampled,  weighed,  and  analyzed  each  day.  The  bread  and 
meat  when  used  are  carefully  sterilized  in  glass  jars.  The  diet  may  be 
so  planned  as  to  maintain  a  uniform  quantity  of  nitrogen  and  a  constant 
calorific  value  from  day  to  day. 

MEASUREMENT  OF  INTAKE  AND  OUTPUT  OF  MATERIAL. 

In  experiments  with  man  as  carried  out  with  this  apparatus  and 
accessories,  the  following  determinations  of  intake  and  output  of  ma- 
terial are  made : 

The  intake  consists  of  food,  drink,  and  oxygen  from  respired  air. 
The  amounts  are  determined  by  weighing.  The  analyses  include  de- 
terminations of  water,  ash,  nitrogen,  carbon,  hydrogen  (organic),  and 
at  times  sulphur  and  phosphorus.  The  output  of  material  consists  of 
products  of  respiration  and  perspiration,  urine,  and  feces.  The  dry 
matter  of  feces  and  urine  is  subjected  to  a  series  of  analyses  similar  to 
those  for  food,  and  the  water  and  carbon  dioxide  of  perspiration  and 
respiration  are  determined  according  to  the  methods  discussed  in  this 
report.  The  determinations  of  nitrogen  in  perspiration  are  made,  when 
necessary,  according  to  methods  given  elsewhere.1 

1  U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations,  Bull.  136,  pp.  52-53. 

12B 


178  A   RESPIRATION    CALORIMETER. 

MEASUREMENT  OF  INTAKE  AND  OUTPUT  OP  ENERGY. 

The  intake  is  derived  from  the  potential  energy,  i.  <?. ,  heats  of  com- 
bustion of  the  food.  The  output  consists  of  sensible  heat  given  off 
from  the  body,  the  latent  heat  of  the  water  vaporized,  and  the  potential 
energy,  i.  <?.,  heat  of  combustion  of  the  unoxidized  portions  of  the  dry 
matter  of  urine  and  feces.  In  certain  cases,  <?.  g. ,  work  experiments,  a 
not  inconsiderable  portion  of  the  output  is  in  the  heat  equivalent  of 
external  muscular  work. 

As  has  been  stated  elsewhere,  the  heats  of  oxidation  are  determined 
by  burning  the  substances  in  the  bomb  calorimeter  ;  the  heat  given  off 
from  the  body  is  measured  by  the  respiration  calorimeter  ;  the  external 
work  is  measured  by  a  specially  devised  ergometer.  Allowance  is  made 
for  heat  introduced  and  removed  by  the  ventilating  air  current,  food, 
feces,  and  urine,  and  for  that  involved  in  changes  of  body  temperature, 
which  is  also  measured. 

ANALYTIC AI,  METHODS. 

The  nitrogen  is  determined  by  the  Kjeldahl  method,  the  carbon  and 
the  hydrogen  by  the  modified  Liebig  method,1  and  the  heats  of  com- 
bustion by  the  bomb  calorimeter.1 

The  observers  work  in  relays  and  all  the  work  is  systematized.  An 
elaborate  system  of  checking  weights  and  observations  serves  to  mini- 
mize errors  or  faulty  manipulation. 

METABOLISM   EXPERIMENT   NO.  70. 

The  particular  experiment  here  used  as  an  illustration  was  not  pre- 
ceded by  the  customary  preliminary  period,  as  it  was  designed  to  study 
metabolism  after  a  period  of  fasting.  The  experiment  shows  the  met- 
abolism on  the  first  day  after  a  5-day  fast. 

Since  it  is  not  the  purpose  of  this  report  to  discuss  metabolism  in 
general,  but  rather  to  describe  the  apparatus  and  methods  of  calcula- 
tion, the  results  for  the  experimental  day  are  here  given  mainly  in  the 
form  of  tables. 

SUBJECT. 

The  subject  was  a  young  medical  student,  B.  A.  S.,  who  had  accus- 
tomed himself  to  periods  of  fasting  varying  from  3  to  10  days.  He 
was  in  excellent  health,  and  previous  to  beginning  his  fast  had  lived  his 
usual  routine  of  life. 

1  Benedict :  Elementary  Organic  Analysis. 

2  Jour.  Am.  Chem.  Soc.  (1903),  25,  p.  659. 


EXPERIMENT  WITH   MAN.  179 

*, 

FOOD. 

On  the  experimental  day  here  reported,  the  diet  consisted  of  1,652.90 
grams  milk  modified  by  a  large  proportion  of  butter  fat,  and  5  grams 
of  the  desiccated  milk  proteid  sold  under  the  trade  name  Plasmon.  In 
addition  to  the  milk  and  Plasmon,  139  grams  of  water  were  used. 
These  quantities  of  food  furnished  53.31  grams  of  protein,  21 1.87  grams 
of  fat,  75.41  grams  of  carbohydrates,  and  2,569  calories  of  energy. 

ROUTINE  OF  EXPERIMENT. 

The  experiment  was  carried  out  according  to  the  customary  routine 
established  in  this  laboratory  for  experiments  with  the  respiration 
calorimeter.  Detailed  accounts  of  this  routine  have  been  published 
elsewhere.1  Minor,  though  important,  changes  in  the  preparation,  sam- 
pling, and  analysis  of  the  milk  and  cream  t/ive  since  been  introduced 
to  facilitate  in  accuracy  and  manipulation. 

The  feces  were  separated  in  the  usual  way  by  means  of  lamp-black 
capsules,  though  in  experiments  either  during  fasting  or  immediately 
following  fasting  we  have  experienced  great  difficulty  in  securing  satis- 
factory separations.  For  the  want  of  more  satisfactory  technique, 
therefore,  we  are  now  in  the  custom  of  collecting  the  total  feces  for  the 
food  period  (in  this  case  3  days),  including  that  passed  after  the  subject 
has  left  the  respiration  chamber,  and  ascribing  an  aliquot  portion  of 
the  feces  to  each  food-day. 

The  daily  routine  followed  by  the  subject  in  the  respiration  chamber 
consisted  mainly  in  rising  from  bed,  dressing,  eating,  care  of  food  and 
excreta,  sitting  at  a  table,  reading  or  writing,  and  occasionally  stand- 
ing or  taking  a  few  short  steps.  In  general,  the  subject  followed  pretty 
closely  a  definite  program  previously  prepared. 

Ordinarily  the  subject  enters  the  respiration  chamber  at  1 1  p.  m.  on 
the  day  before  the  actual  experiment  begins.  This  enables  him  to 
become  accustomed  to  the  environment,  and  affords  opportunity  to 
secure  constant-temperature  conditions  inside  the  chamber  after  a  long 
night's  sleep.  In  this  particular  case,  the  subject  had  already  remained 
in  the  chamber  for  5  days  of  fasting,  so  that  there  was  no  preliminary 
period  for  the  food  experiment,  which  began  at  7  a.  m.  From  this  time 
to  the  close  of  the  experiment  a  careful  record  was  kept  of  all  data 
for  computing  the  total  income  and  outgo  of  matter  and  energy.  So 
far  as  the  measurements  of  heat,  carbon  dioxide,  water,  and  oxygen 
are  concerned,  the  day  was,  as  usual,  divided  into  12  periods  of  2  hours 
each.  It  has  not  been  found  feasible  to  make  such  short  separations 

1 U.  S.  Dept.  of  Agr.,  Office  of  Experiment  Stations  Bulls.  44,  63,  69,  109,  and  136. 


i8o 


A    RESPIRATION   CALORIMETER. 


of  the  urine,  and  consequently  the  analyses  are  not  made  on  periods 
shorter  than  24  hours,  save  in  the  case  of  determinations  of  total  nitrogen, 
which  are  at  times  made  on  6-hour  periods. 

STATISTICS  OF  FOOD,  FECES,  AND  URINE. 

In  Table  5  the  percentage  composition  of  the  food  materials,  feces, 
and  urine  are  given. 

TABLE  5. — Percentage  Composition  of  Food  Materials,  Feces,  and  Urine, 
Metabolism  Experiment  No.  70. 


:ub. 

No. 

Material. 

(«) 
Water. 

b 
Protein. 

W 

Fat. 

(d) 
Carbo- 
hydrates. 

M 

Ash. 

(/) 
Nitro- 
gen. 

Cf) 

Carbon. 

(h) 
Hydro- 
gen. 

(0 

Energy 
per  gram. 

4806 

Milk.... 

Per  ct. 

79.14 

Perct. 
3.00 

Perct. 
12.63 

Per  ct. 

4.59 

Per  ct. 

o  64 

Per  ct. 

o  48 

Per  ct. 
12  86 

Per  ct. 

Calories. 

3807 

3773 

do  
Plasmon  

78.46 
9.80 

srj 

74.50 

I3-56 
0.15 

4-35 
6.88 

0.63 
8.67 

0.48 
11.92 

13-50 

2.IO 
6.14 

A  820 

3819 

Feces  

6639 

3.71 

2.78 

20.15 

6.97 

0.59 

1Q.75 

V*3 

2.447 

•*8i"; 

Urine  

96  ii 

o  86 

These  values  are  determined  directly  in  the  case  of  water,  fat,  ash, 
nitrogen,  carbon,  and  hydrogen.  The  protein  is  obtained  from  the 
nitrogen  by  multiplying  by  the  factor  6.25.  The  carbohydrates  are 
determined  by  difference.  The  heat  of  combustion  per  gram  is  deter- 
mined by  combustion  in  the  bomb  calorimeter. 

In  all  cases  except  that  of  the  feces  the  materials  are  analyzed  on 
the  fresh  basis,  i.  e.,  original  weights  are  on  the  fresh  material.  The 
feces  of  necessity  are  analyzed  after  drying. 

The  total  amounts  of  food,  with  the  quantities  of  nutrients  and  energy 
supplied,  are  shown  in  Table  6. 

TABLE  6. —  Weight,  Composition,  and  Heat  of  Combustion  of  Food,  Metabolism 

Experiment  No.  70. 


Lab. 

No. 

Food 
material. 

(a) 

Total 
weight. 

(b) 
Water. 

Water-free  substance. 

(c) 
Pro- 
tein. 

(d) 
Fat. 

w 

Car- 
bohy- 
drates. 

(/) 
Ash. 

M 

Nitro- 
gen. 

(h) 

Car- 
bon. 

(') 

Hy- 
dro- 
gen. 

(J) 
Oxy- 
gen. 

w 

Energy. 

3806 
3807 
3773 

Milk  

Cms. 
1,320.10 
332-80 
5.00 

Cms. 
1.044.73 
261.11 
0.49 

Cms. 

396o 
9.98 
3-73 

Gms. 

166.73 
45-13 

O.OI 

Gms. 
60.59 
14.48 
0-34 

Gms. 

8-45 

2.10 
0-43 

Gms. 

6-34 
i.  60 
0.60 

Gms. 

169.76 
44-93 

2.21 

Cms 

26.40 
6.99 
031 

Gmi>. 
64.42 
16.07 
0.96 

Calories. 
2,013 
532 
24 

do  
Plasmon  

Total... 

1,657.90 

-,306.33 

53-31 

211.87 

75-41 

10.98 

8-54 

2l6.0X> 

33-70 

81.45 

2,569 

For  purposes  of  further  computation  the  amount  of  oxygen  in  the 
water- free  substance  of  the  food  is  here  given,  though  obviously  this 
is  a  result  of  indirect  determination. 


EXPERIMENT   WITH   MAN. 

Similar  data  for  the  feces  and  urine  are  given  in  Table  7. 


181 


TABLE  7. —  Weight,  Composition ,  and  Heat  of  Combustion  of  Urine  and  Feces 
Metabolism  Experiment  No.  70. 


(«) 

Total 
weight. 

(*) 
Water. 

Water-free  substance. 

to 

Ash. 

w 

Nitrogen. 

to 
Carbon. 

(/) 
Hydrogen. 

Or) 

Oxygen. 

(A) 
Energy. 

Urine  

Grants. 
1,031.50 
60.97 

Grams. 
991-37 
40.48 

Grams. 
4.54 
4-25 

Grams. 
13.04 
0.36 

Grams. 
8.87 
12.04 

Grams. 
2-37 
1.91 

Grams. 
11.31 
1-93 

Calories. 
103 
149 

Feces  

The  amount  of  oxygen  in  the  water-free  material  is  also  included  in 
the  table  for  subsequent  use. 

Summaries  of  the  data  for  the  determination  of  water,  carbon  dioxide, 
and  oxygen  are  given  in  Tables  8  to  10. 

STATISTICS  OF  WATER  ELIMINATED. 

The  quantities  of  water  exhaled  by  the  subject  during  each  experi- 
mental period  are  calculated  from  the  determinations  of  the  amount  of 
water  removed  from  the  ventilating  air  current  and  the  difference 
between  the  quantity  remaining  in  the  air  inside  the  apparatus  at  the 
beginning  and  end  of  the  period.  These  computations  are  summarized 
in  Table  8. 

TABLB  8. — Record  of  Water  in  Ventilating  Air  Current,  Metabolism  Experiment, 

No.  70. 


(«) 

(*) 

(c) 

(d) 

(') 

(/) 

Or) 

Change 

Total 

Total 

Date. 

Period. 

amount 
of  vapor 
in  cham- 
ber at 
end  of 
period. 

Gain  (+) 
or 
loss  (  -  ) 
over  pre- 
ceding 
period. 

weight 
of  heat- 
absorb- 
ing sys- 
tem — 
gain  (+), 
loss  (  —  ). 

Change 
in 
weight 
of  chair, 
bedding, 
etc. 

amount 
gained 
(+)or 
lost(-) 
during 
period. 
(6+c+d) 

Total 
amount 
in 
out- 
going 
air. 

water 
of  respi- 
ration 

and  per- 
spira- 
tion. 
<*+/)* 

1904. 

Grams. 

Grams. 

Grams. 

Grams. 

Grams. 

Grams. 

Grams. 

Dec.  20 

5  a.  m  to   73.  m.. 

36.07 

Dec.  20-21 

7  a.  m  to   9  a.  m.. 

38  74 

+  2  67 

71  87 

9  a.  m  to  ii  a.  m.. 

39.91 

+  1.  17 

66  7Q 

ii  a.  m  to    i  p.  m.. 

38.91 

—  1.  00 

67^5 

66.55 

i  p.  m  to   3  p.  m.. 

41.73 

+  2.82 

61.85 

6467 

3  p.  m  to   5  p.  in.. 

36.93 

—  4.80 

6895 

64.15 

5  p.  m  to   7  p.  m.. 

37.76 

+  083 

7  p.  m  to   9  p.  m.. 

37-28 

—  0.48 

65.96 

65.48 

9  p.  m  to  ii  p.  m.. 

37.23 

—  O.O5 

66.26 

66  21 

ii  p.  m  to    la.  m.. 

39-97 

i  a.  m  to    3  a.  m.. 

46.06 

+  6.OQ 

84.41 

3  a.  m  to   53.  m.. 

39-71 

-6-35 

76.55 

70.20 

5  a.  m  to    73.  m.. 

33-18 

-6-53 

70.31 

63.78 

Total  

—  2  80 

•4-  *  26 

*8j8  30 

*The  total  for  this  column  is  the  sum  of  (e)  +  (/). 


1 82  A    RESPIRATION   CALORIMETER. 

The  quantity  of  water  removed  from  the  air  current  during  each  period 
is  determined  by  weighing  the  water- absorbers  at  the  beginning  and  end 
of  the  period.  The  values  thus  found  are  expressed  in  column  (/"). 
The  quantity  of  water  in  the  air  remaining  in  the  chamber  at  the  end 
of  each  period  is  learned  by  analysis  of  a  sample  of  the  air.  These 
determinations  are  given  in  column  (a).  The  increase  or  decrease  in 
the  quantity  of  vapor  residual  in  the  air  for  each  period,  which  is  simply 
the  difference  between  the  quantity  at  the  end  of  one  period  and  that 
at  the  end  of  the  next,  is  given  in  column  (£) ,  an  increase  being  indi- 
cated by  +  and  a  decrease  by  — . 

The  quantity  of  water  exhaled  by  the  subject  during  each  period, 
shown  in  column  (g},  is  the  algebraic  sum  of  the  quantities  in  columns 
(£)  and  (/).  If  the  value  is  indicated  by  +  in  column  (£)  it  is  added, 
because  it  represents  an  excess  that  has  been  added  by  the  subject 
during  the  period  ;  it  is  subtracted  when  the  sign  is  — ,  because  that 
means  that  the  absorbing  apparatus  has  removed  from  the  air  so  much 
more  than  was  exhaled  by  the  subject. 

As  a  result  of  the  variation  in  hygrometric  conditions  inside  the  respi- 
ration chamber,  there  may  be  a  noticeable  change  in  the  amount  of 
moisture  deposited  upon  the  bedding,  clothing,  etc.,  of  the  man  and 
also  upon  the  heat-absorbing  system.  In  general,  this  latter  is  negli- 
gible in  the  case  of  the  rest  experiments,  such  as  experiment  No.  70 
reported  here.  On  the  particular  day  here  given  there  was  a  loss 
of  weight  in  the  heat-absorbing  system  amounting  to  2  grams,  and  an 
increase  in  weight  of  the  chair,  bedding,  etc. ,  of  5. 26  grams.  These  are 
recorded  in  columns  (c)  and  (aT),  Table  8.  In  column  (e)  the  algebraic 
sum  of  (£),  (c)t  and  (d}  is  given.  Obviously,  for  the  entire  day  the 
total  water  of  respiration  and  perspiration  is  the  algebraic  sum  of  (tf) 
and  (/)  and  not  of  (6)  and  (/). 

STATISTICS  OF  CARBON  DIOXIDE  ELIMINATED. 

The  determinations  of  the  quantity  of  carbon  dioxide  exhaled  by  the 
subject  during  each  period  depend,  like  those  for  water,  upon  the  quan- 
tity removed  from  the  ventilating  air  by  the  absorbers  and  that  remain- 
ing in  the  air  within  the  apparatus.  These  data  for  carbon  dioxide  are 
summarized  in  Table  9.  The  determinations  of  the  total  quantity  of 
carbon  dioxide  removed  from  the  air  current  during  an  experimental 
period,  ascertained  by  weighing  the  absorbing  apparatus  at  the  beginning 
and  end  of  each  period,  are  shown  in  column  (V).  The  quantities  of 
carbon  dioxide  remaining  in  the  air  of  the  chamber  at  the  end  of  each 
period,  as  determined  by  analysis  of  a  sample  of  the  air,  are  shown  in 
column  (a).  The  difference  between  the  quantity  residual  in  the  air 
at  the  end  of  one  period  and  that  at  the  end  of  the  next  period  is  shown 


EXPERIMENT  WITH   MAN. 


183 


in  column  (£) ,  with  a  plus  sign  to  indicate  a  gain  and  a  minus  sign  a 
loss  in  the  residua!  amount  in  the  air  during  the  given  period.  The 
total  amount  of  carbon  doxide  given  off  by  the  subject,  as  shown  in 
column  (d),  is  the  sum  of  the  quantities  in  columns  (£)  and  (V). 

9. — Record  of  Carbon  Dioxide  and  Carbon  in  Ventilating  Air  Current, 
Metabolism  Experiment  No.  70. 


Date. 

Period. 

Carbon  dioxide. 

(/) 

Carbon 
in  carbon 
dioxide 
exhaled. 
(rfX3/"> 

(«) 

Amount 
in  cham- 
ber at 
end  of 
period. 

(*) 

Gain(-f) 
or  loss 
(—  )  over 
preced- 
ing 
period. 

(c) 

Amount 
absorbed 
from  out- 
coming 
air. 

(d) 

Corrected 
weight 
exhaled 
by 
subject. 
l*+«J 

w 

Volume 
exhaled 
by  subject. 
(dX  0.5091) 

1904. 
Dec.  20 
Dec.  20-21 

Grams. 

Grams. 

Grams. 

Grams. 

Liters. 

Grams. 

33-47 
5I-I9 
37-97 
55-.S9 
39  '3 
33-°3 
37-32 
30.80 
28.76 
2683 
28.03 
21.96 

5.63 

69.24 

42.35 
68.71 
42.10 
73.67 
66.17 
55-68 
60.02 

53-45 
51.04 
40.41 
47.16 

63.61 
60.07 
55-49 
59-72 
57-21 
60.07 
59-97 
53-50 
5'.4i 
49.11 
41.61 
41.09 

32.38 
30.58 
28.25 
30.40 
29.13 
30-58 
30.53 
27.24 
26.17 
25.00 
21.  18 
20.92 

17-35 
16.38 
15-13 
16.29 
15.60 
16.38 
16.36 

14-59 
14.02 

13.39 
".35 

II.  21 

9  a.  in   to  ii  a.  m  

+  17-72 
—  13.22 
+  17.62 
—  16.46 
—    6.10 
+    4-29 

6  12 

ii  a.  in  to    i  p.  m  

i  p.  in    to    3  p.  ro  

3  p.  m   to   5  p.  m  

5  p.  m  to    7  p.  m  

7  p.  m  to   9  p.  m  

ii  p.  m  to    i  a.  in  

—  2.04 

—    1-93 
-f-    1.  20 
—    6.07 

i  a.  m   to   3  a.  m  

3  a.  in   to   5  a.  m  

5  a.  m  to    73.  111  

Total  

—  I7-H 

670.00 

652.86 

332-36 

178.05 

In  computing  the  respiratory  quotients  given  in  Table  10,  it  is  neces- 
sary that  the  quantities  of  carbon  dioxide  exhaled  by  the  subject  be 
expressed  in  volume  rather  than  in  weight.  These  values  are  shown 
in  column  (c)  in  Table  9,  which  are  obtained  from  those  in  column  (d) 
by  the  factor  expressing  the  relation  of  volume  to  weight  of  carbon 
dioxide.  The  quantities  of  carbon  in  the  carbon  dioxide  exhaled  by 
the  subject  during  each  period,  which  are  likewise  used  in  computations 
of  later  tables,  are  shown  in  column  (/).  These  values  are  calculated 
directly  from  those  in  column  (a?) . 

STATISTICS  OF  OXYGEN  CONSUMED. 

The  quantity  of  oxygen  consumed  by  the  subject  during  each  period 
is  learned  from  the  determinations  of  the  quantity  admitted  from  the 
cylinders  to  the  chamber  and  that  remaining  in  the  air  at  the  end  of  the 
period.  These  data  are  summarized  in  Table  10. 

The  amount  of  oxygen  supplied  during  each  period  is  determined  by 
the  loss  in  weight  of  the  cylinder  between  the  beginning  and  end  of  the 
period  and  the  purity  of  the  oxygen  in  the  cylinder,  and  is  recorded 
in  column  (</). 


184 


A   RESPIRATION   CALORIMETER. 


The  quantity  of  oxygen  in  the  air  of  the  chamber  at  the  beginning 
and  end  of  each  day  is  learned  by  analysis  of  samples  of  the  air  taken 
at  7  a.  m.,  and  is  given  in  column  (a).  Similar  values  for  the  different 
experimental  periods,  given  in  the  same  column,  are  found  by  calcula- 
tion, as  explained  on  page  95. 

The  quantities  in  column  (^)  represent  the  increase  or  decrease  in  the 
oxygen  content  of  the  air  during  the  different  periods.  These  are 
expressed  by  volume  in  column  (6)  and  by  weight  in  column  (c).  The 
algebraic  difference  between  the  quantities  in  columns  (af )  and  (V)  is  the 
amount  consumed  by  the  subject. 

TABLE   10. — Record  of  Oxygen   in    Ventilating  Air  Current  and  Respiratory 
Quotients  by  Periods,  Metabolism  Experiment  No.  70. 


Oxygen. 

Period. 

(«) 
Total 
amount 
in  cham- 
ber at 
end  of 
period. 

Gain  (+)  or  loss 
(—  )  during  period. 

M 

Amount 
admitted 
to 
cham- 
ber. 

(e) 
Corrected 
amount 
consumed 
by 
subject. 
(d-c) 

\J) 
Volume 
of 
oxygen 
con- 
sumed 
(«Xo.7) 

(£) 
Volume 
of 
carbon 
dioxide 
exhaled. 

(") 

Respira- 
tory 
quotient. 

Or-/) 

(*) 
Volume. 

(c) 
Weight. 
(«-=-o.7) 

Dec.  20,  1904. 

Liters. 

Liters. 

Grams. 

Grams. 

Grams. 

Liters. 

Liters. 

Dec.  20-21,  1904. 

7  a.  m.  to   9  a.  m.. 

9r3.54 

+   6.26 

+   8.94 

72-34 

63.40 

44.38 

32-38 

0.7296 

9  a.  ra.  to  ii  a.  m.. 

899.46 

—  14.08 

—  20.  i  r 

36.78 

56.89 

39.82 

30.58 

0.7680 

ii  a.  m.  to    i  p.  ra.. 

898.36 

—     1.  10 

—   i-57 

52-49 

54-o6 

37-84 

28.25 

0.7466 

i  p.  m.  to   3  p.  in.. 

881.96 

—  16.40 

—  23-43 

33-74 

57.17 

40  02 

30.40 

0.7596 

3  p.  m.  to   5  p.  m.. 

8<9.44 

+   7.48 

+  10.69 

62.36 

51-67 

36.17 

29-13 

0.8054 

5  p.  m.  to   7  p.  m.. 

88834 

—     l.IO 

—   1-57 

57-97 

59-54 

41.68 

30.5« 

0.7337 

7  p.  m.  to   9  p.  m.. 

8*1.65 

—  6.69 

—   9-56 

46.66 

56.22 

39-3S 

30.53 

0.7759 

9  p.  m.  to  1  1  p.  m.. 

878.59 

—   3-o6 

—   4-37 

48.47 

52.84 

36.99 

27.24 

0.7364 

ii  p.  m.  to    i  a.  m.. 

871.47 

—   7-12 

—  10.17 

39-09 

49.26 

34-48 

26.17 

0.7590 

i  a.  m.  to   3  a.  m. 

871.10 

—  0-37 

—  0.53 

48.38 

48-9I 

34-24 

25.00 

0.7301 

3  a.  m.  to   5  a.  m.. 

879.  10 

+    8.00 

+  H-43 

48.42 

36.99 

35.89 

21.  18 

08181 

5  a.  m.  to   7  a.  m.. 

907.04 

-f  27.94 

+  39-91 

75-36 

35-45 

24.82 

20  92 

0.8429 

Total  

-   0.34 

622.06 

622.40 

435-68 

332.36 

0.7629 

RESPIRATORY  QUOTIENT. 

The  ratio  between  the  volume  of  carbon  dioxide  exhaled  and  the 
volume  of  the  oxygen  inspired,  and  indicating  in  marked  degree  the 
nature  of  the  materials  burned  inside  the  body,  is  commonly  called  the 
respiratory  quotient.  In  the  experiments  with  men,  it  is  computed  on 
the  sheets  upon  which  are  recorded  the  data  for  the  determinations  of 
the  amount  of  oxygen  consumed,  Table  10,  and  is  recorded  in  column 
(^).  In  determining  the  respiratory  quotient,  the  weight  of  carbon 
dioxide  found  is  converted  to  liters  by  multiplying  by  the  factor  0.5091 , 
column  (tf) ,  Table  9,  while  the  weight  of  oxygen  absorbed  by  the  bodj' 
is  converted  to  liters  by  multiplying  by  0.7,  column  (/)  of  Table  10. 
The  ratio  between  the  volumes  of  carbon  dioxide  eliminated  and  oxygen 
absorbed,  CO2-v-  O2,  represents  the  so-called  "  respiratory  quotient." 


EXPERIMENT   WITH   MAN. 


185 


When  carbohydrates  are  burned  in  the  body,  the  volume  of  oxygen 
consumed  is  equal  to  the  volume  of  carbon  dioxide  given  off,  since 
the  hydrogen  and  oxygen  in  the  carbohydrate  molecule  are  in  the 
same  proportions  as  in  water,  and  in  the  conversion  of  carbon  to 
carbon  dioxide  the  volume  of  carbon  dioxide  is  invariably  the  same  as 
the  volume  of  oxygen  required.  In  the  case  of  the  proteids,  where 
not  only  carbon  is  oxidized,  but  also  some  hydrogen,  it  is  found  that 
the  respiratory  quotient  is  generally  not  far  from  0.809,  while  in  the 
case  of  fats,  where  the  amount  of  hydrogen  oxidized  is  quite  consider- 
able, the  respiratory  quotient  may  fall  as  low  as  0.711.  It  has  been 
found  as  a  result  of  experimenting  with  other  types  of  respiration 
apparatus,  especially  those  of  Zuntz  and  Chauveau  (see  p.  3),  that 
the  respiratory  quotient  on  an  ordinary  mixed  diet  is  not  far  from  0.9. 
From  an  inspection  of  column  (^)  of  Table  10  of  experiment  70  given 
herewith,  it  will  be  seen  that  the  large  proportion  of  fat  in  the  diet  re- 
sulted in  a  marked  lowering  of  the  respiratory  quotient. 

SUMMARY  OP  CALORIMETRIC  MEASUREMENTS. 

The  records  of  the  heat  measurements  by  means  of  the  respiration 
calorimeter  are  summarized  in  Table  n. 

n. — Summary  of  Calorimetric  Measurements,  Metabolism  Experiment 

No.  70. 


(«) 

(*) 

(c) 

<<*) 

(') 

(/) 

M 

Water 

Period. 

Heat 
meas- 
ured in 
terms 

c». 

Change 
in 
tempera- 
ture of 
calo- 
rimeter. 

Capacity 
correc- 
tion 
of  calo- 
rimeter. 

Correc- 
tion due 
to  tem- 
perature 
of  food 
and 

vapor- 
ized 
equals 
total  in 
outgoing 
air  plus 
excess 

Heat  used 
in  vapori- 
zation of 
water. 
(e  X  0.592) 

Total  heat  de- 
termined. 
(a  +  c  +  d+/) 

disnes. 

residual 

vapor. 

Dec  20-21,  1904. 

Calories. 

Degrees. 

Calories. 

Calories. 

Grams. 

Calories. 

Calories. 

7  a.  m  to   9  a.  m 

172.35 

+  0.03 

+    i.So 

+  9-22 

74-54 

44-13 

227.50 

9  a.  m  to  ii  a.  m 

132-56 

—  0.05 

—   3.00 

+   2.87 

66.39 

39-30 

171  73 

ii  a.  m  to    i  p.  m 

122.23 

+  0.03 

+    i.  80 

+  12.02 

66.55 

39-40 

175-45 

6d  67 

38.28 

178.69 

3  p.  m  to   5  p.  m 

149.84 

+  0.02 

+    i.  20 

+  4-37 

"*•"' 
64.15 

37-98 

I9J-39 

5  p.  m  to   7  p.  m 

I5I-31 

4-  o  oi 

+    0.60 

+  8.23 

70.53 

41-75 

201.89 

7  p.  m  to   9  p.  m 

148.42 

—  O.O7 

—   4.30 



65.48 

38-76 

182.98 

9  p.  m   to  up.  m 

132.43 

+  O.O2 

+    i.  20 

66.21 

^0.2O 

172-83 

ii  p.  m  to    i  n.  01 

TT  C  6d 

+  O.O5 

+    3.00 

72.04 

OV*" 
42.6^ 

161.29 

i  a.  m  to   3  a.  m  

*  *O'*-"T 

112.25 

—  0.06 

—   3-6o 

90.50 

'•v/O 

5358 

162.23 

3  &.  tn  to   5  a.  m  

118  10 

+  O  1^ 

+    7-8o 

70.20 

41  s6 

167.46 

5  a.  m  to   ?a.  m  

98.85 

1     v-*o 

—  0.31 

—  18.60 

63.78 

4-*-O" 

37-76 

118.01 

Total  

1,595.  59 

—  O.22 

—  13.20 

+36.71 

835.04 

494-35 

2,113.45 

The  major  part  of  the  heat  generated  within  the  apparatus  is  absorbed 
and  carried  away  by  a  current  of  cold  water  through  the  heat- absorbers. 
The  quantity  of  heat  thus  brought  out  is  determined  from  measurement 


1 86  A   RESPIRATION   CALORIMETER. 

of  the  amount  of  water  which  flows  through  the  absorbers  and  the 
difference  between  the  temperature  of  the  water  as  it  enters  and  as  it 
leaves  the  chamber.  These  determinations  are  given  in  column  (a). 

Part  of  the  heat  generated  within  the  respiration  chamber  is  brought 
away  as  latent  heat  of  the  water  vapor  carried  out  in  the  ventilating  air 
current.  The  amount  of  heat  brought  out  in  this  way,  being  simply  the 
amount  necessary  to  vaporize  the  water,  is  calculated  from  the  amount 
of  water  vaporized.  The  amount  of  water  vapor  for  each  experimental 
period,  shown  in  column  (e~),  is  taken  from  column  (g~)  of  Table  8,  and 
the  amount  of  heat  necessary  to  vaporize  it  is  calculated  from  the  quan- 
tities in  column  (>)  by  use  of  the  factor  o.  592  as  the  latent  heat  of  vapor- 
ization of  water  per  gram.  These  values  are  given  in  column  (./). 

In  addition  to  the  above,  a  certain  amount  of  heat  is  concerned  in  the 
changes  in  temperature  of  the  walls  of  the  respiration  chamber  and 
other  parts  of  the  apparatus.  Each  degree  of  change  of  temperature  for 
the  whole  calorimeter  is  assumed  to  represent  60  calories  of  heat.  The 
difference  between  the  initial  and  final  temperatures  of  each  period  gives 
the  total  change  of  temperature  to  be  taken  into  account.  These  data 
are  shown  in  column  (3).  Multiplying  these  values  by  60  gives  the 
total  quantity  of  heat  involved  in  the  changes  of  temperature,  as  shown 
in  column  (c). 

Food  materials,  dishes,  etc.,  when  sent  into  the  chamber  through 
the  food  aperture,  of  course  deliver  heat  when  they  are  warmer  than 
the  air  of  the  chamber,  and  remove  heat  by  absorption  when  they  are 
cooler.  The  amount  of  heat  thus  introduced  or  removed  during  the 
different  periods  of  the  experiment,  as  calculated  from  the  weight  and 
specific  heat  of  each  material  and  the  difference  between  its  temperature 
and  that  of  the  chamber,  is  shown  in  column  (d~). 

The  total  amount  of  heat  determined  in  an  experimental  period, 
column  (£-),  is  therefore  the  algebraic  sum  of  the  quantities  of  heat 
brought  away  by  the  circulating  water  current,  as  shown  in  column  (a), 
with  the  correction  due  to  changes  in  temperature  of  the  calorimeter, 
column  (V),  the  correction  for  heat  removed  or  introduced  by  food, 
dishes,  etc.,  column  (cT)t  and  the  heat  latent  in  the  water  vaporized, 
column  (/"). 

It  should  be  added  that  the  temperature  of  the  ventilating  air  current 
is  so  regulated  as  to  be  the  same  in  entering  as  in  leaving,  so  that  it 
carries  out  the  same  amount  of  heat  as  it  brings  in,  and  need  not  be 
taken  into  account  in  the  tables. 

No  corrections  have  been  made  for  variations  in  heat  measurement 
due  to  changes  in  body  temperature,  changes  in  body  weight,  or  to  the 
absorption  and  radiation  of  heat  by  the  bed  and  bedding,  as  previously 


EXPERIMENT  WITH   MAN. 


187 


explained.  These  corrections  are  chiefly  of  importance  from  their  bear- 
ing upon  the  question  of  heat  production  versus  heat  elimination,  and 
they  are  accordingly  omitted  from  the  present  brief  summary. 

INTAKE  AND  OUTPUT  OF  MATERIAL,  AND  ENERGY. 

From  the  data  derived  from  the  preceding  tables  the  balance  between 
the  intake  and  output  of  material  and  energy  in  the  body  may  be  cal- 
culated. The  methods  and  results  of  these  calculations  may  be  explained 
as  follows  : 

GAINS   AND   LOSSES  OF  BODY   MATERIAL. 

In  order  to  compute  the  gains  and  losses  of  body  material  as  expressed 
in  terms  of  protein,  fat,  and  carbohydrates  it  is  necessary  first  to  deter- 
mine the  gains  and  losses  of  the  elements  which  make  up  these  com- 
pounds. This  is  done  by  comparing  the  amounts  of  the  elements  in 
the  intake  of  the  body  with  those  of  the  output,  as  shown  in  Table  12. 

12. — Gain  or  Loss  of  Body  Material,  Metabolism  Experiment  No.  70. 


(a) 
Total 
weight. 

<*) 
Nitrogen. 

w 

Carbon. 

(rf) 
Hydro- 
gen. 

GO 
Oxygen. 

(/) 
Ash. 

Intake. 

Grams. 
622.40 

Grams. 

Grams. 

Grams. 

Grams. 
622.40 

Grams. 

139.00 

15.55 

123.45 

Water  in  food  

1,306.33 
351.57 

854 

216  90 

146.18 
33.70 

1,160.15 
81.45 

10.  qS 

Total  

2,419.30 

8.54 

216.90 

195.43 

1,987.45 

10.98 

Output. 

40.48 

4-53 

35-95 

20.49 

0.36 

12.04 

1.91 

1.93 

4.25 

991.37 

110.94 

880.43 

40.13 

13.04 

8.87 

2.37 

11.31 

4-54 

838.30 

93.81 

744  49 

COa  of  respiration  

652.86 

178.05 

474.81 

Total    

2,583.63 

13.40 

198.96 

213.56 

2,148.92 

8.79 

4  86 

—  18.13 

+  2.19 

—  0.45 

—  164  78 

+  1-74 

Gain  or  Loss  of  Body  Material. 

—  4  86 

—    2.04 

—     6.41 

—  0.45 

Fat  ... 
Glycogen  
Water               .  ...                        

+    33-54 
+    17-53 
18888 

+  25-52 
+    7-78 

+    3-96 
+    i.°9 
—  21.14 

+     4.06 
+      8.66 
—  167  74 

Ash          

+  2-J9 

Total  

—  164.78 

—  4.86 

+  17.90 

—  18.13 

—  161.43 

+  1-74 

The  intake  of  the  body  is  made  up  of  the  following:  (i)  Oxygen 
from  the  air,  which  is  found  for  this  experiment  in  column  (<?)  of  Table 
10  ;  (2)  water  in  drink,  which  is  taken  from  the  record  of  the  amount 


i88 


A    RESPIRATION    CALORIMETER. 


of  water  consumed  during  the  experiment ;  (3)  water  of  food,  which 
is  taken  from  column  (£)  of  Table  6  ;  (4)  solids  of  food,  the  quantity 
of  which  is  determined  as  the  difference  between  the  total  weight  of 
food  material  and  the  weight  of  water  which  it  contains,  as  shown  by 
columns  (a)  and  (£)  of  Table  6.  In  such  computations  milk  is  con- 
sidered as  food  rather  than  as  drink. 

The  output  consists  of  (i)  water  and  (2)  solids  of  feces  and  (3)  water 
and  (4)  solids  of  urine,  which  are  all  obtained  by  simple  computation 
from  columns  (a)  and  (£)  of  Table  7  ;  (5)  water  of  respiration  and  per- 
spiration, which  is  obtained  from  column  (^)  of  Table  8,  and  (6)  car- 
bon dioxide  obtained  from  column  (d)  of  Table  9. 

The  quantity  of  oxygen  consumed  by  the  subject  from  the  air  is 
directly  determined.  The  quantities  of  hydrogen  and  oxygen  in  the 
water  of  drink,  food,  feces,  urine,  and  respiration  are  calculated  from 
the  composition  of  water,  and  the  quantities  of  carbon  and  oxygen  in 
the  carbon  dioxide  exhaled  by  the  subject  are  calculated  from  the 
composition  of  carbon  dioxide.  The  quantities  of  nitrogen,  carbon, 
hydrogen,  oxygen,  and  ash  of  solids  of  food,  feces,  and  urine  are  taken 
from  Tables  6  and  7,  respectively. 

The  differences  between  the  amounts  of  the  elements  of  intake  and 
those  of  output  show  how  much  of  each  was  gained  or  lost.  Compu- 
tation of  the  gains  or  losses  of  protein,  fat,  carbohydrates,  and  water 
from  those  of  the  elements  depends  upon  the  elementary  composition  of 
the  compounds. 

The  values  for  percentage  composition  employed  in  these  investiga- 
tions are  as  follows  : 


Body  material. 

N. 

C. 

H. 

o- 

Mineral 
matters 

(includ- 
ing  8). 

Proteids  

Per  cent. 
16.67 

Per  cent. 
52.86 

Per  cent. 
7  oo 

Per  cent. 
22.OO 

Per  cent. 
I  W 

Pat  

76.IO 

II.  So 

12  IO 

Carbohydrates      

AA   ACt 

6  20 

AQ  AT) 

Water  

II.  IQ 

88.81 

Disregarding  the  mineral  matters,  the  following  equations  may  be 
derived  from  the  above  data,  letting  p  =  protein,  /=  fat,  r=  carbohy- 
drates, and  w  =  water  : 


0.4440  r  +  0.7610  /  4-  0.5280  p  —  C 
0.1119  w  +  0.0620  r  +/3.n8o  t  +  0.0700  /  =  H 
0.8881  w  4-  0.4940  r  4-  0.1210  /  4-  0.2200  /  =  O 


EXPERIMENT  WITH   MAN. 


189 


Solving  these  equations  in  terms  of  N,  C,  H,  and  O,  the  following 
formulae  are  obtained  : 

Protein  =  6.0  N 

Fat  =  0.005  C  +  9-693  H  —  i.  221  O  —  2.476  N 
Carbohydrates  =  +  2.243  C  —  16.613  H  +  2.093  O  —  2.892  N 
Water  =  —  1.248  C+  7.920  H  +  0.128  O  +  0.460  N 

Substituting  for  the  elements  in  these  formulae  the  quantity  of  each 
gained  or  lost  as  expressed  in  grams  in  Table  1  2  ,  and  performing  the 
calculations,  gives  the  weights  of  the  compounds  gained  or  lost.  In 
the  following  illustration  the  figures  are  taken  from  the  data  for  the 
first  day  of  the  experiment  (Table  12).  Thus  : 

Protein  =  6  N 

=  6  (—4.86) 
=  —  29.16 

indicating  that  29.16  grams  of  protein  were  lost  on  that  day.     Again  : 

Fat  =  +  0.005  C  +  9.693  H  —  1.221  O  —  2.476  N 

=•  +  0.005  (-I7-94)    +9-693  (—18.12)    —  1.221  (—161.48)—  2.476  (—4.86) 
=  +  0.090  —  175.637  +  197-167  +  12.033 


indicating  that  33.65  grams  of  fat  were  lost  on  that  day.  The  results 
for  carbohydrates  and  water  are  derived  in  the  same  way  from  the 
other  two  formulae. 

The  results  as  thus  computed  are  given  in  the  bottom  division  of 
column  (a)  of  Table  12.  The  correctness  of  the  computations  is  tested 
mathematically  as  follows  :  From  the  total  weight  of  each  compound 
gained  or  lost  and  its  percentages  of  the  elements  assumed  in  the  tabular 
statement  above,  the  quantities  of  the  elements  gained  or  lost  are  com- 
puted. The  total  for  each  element  thus  derived  should  be  the  same 
as  the  difference  between  the  income  and  outgo  of  the  same  element. 

The  gains  or  losses  of  material  expressed  in  terms  of  chemical  ele- 
ments and  protein,  fat,  carbohydrates,  and  water  are  summarized  in 
Table  13. 

TABI,B  13.  —  Gain  or  Loss  of  Elements  and  Protein,  Fat,  Carbohydrates,  and  Water, 
Metabolism  Experiment  No.  70. 


Nitrogen. 

Carbon. 

Hydrogen. 

Oxygen. 

Protein. 

Fat. 

Carbo- 
hydrates. 

Water. 

December  20  ... 

Grams. 

-4-86 

Grams. 

+  17-94 

Grams. 
—  18.12 

Grams. 
—  161.48 

Grams. 
—  29.16 

Grams. 
+  33.65 

Grams. 

+  17-34 

Grams. 

—  188.80 

i  go 


A    RESPIRATION    CALORIMETER. 
BODY  WEIGHT. 


The  figures  of  Table  12  imply  that  the  body  lost  164.78  grams  of 
material  during  the  experiment.  If  there  were  no  experimental  errors 
the  body  should  have  weighed  164.78  grams  less  at  the  end  than  at  the 
beginning  of  the  experiment.  This  calculated  balance  was  checked 
by  actual  weighings  of  the  body. 

TABI,E  14. — Balance  of  Gains  and  Losses  of  Body  Material  and  Gain  and  Loss  of 
Body  Weight^  Metabolism  Experiment  No.  70. 


Intake. 

Output. 

Balance. 

Gain 

Gain 

Food. 

Water. 

Oxy- 
gen. 

Total. 

Urine. 

Feces. 

CO,. 

Water. 

Total. 

or  loss 
(-)of 
body 

or  loss 
(-)of 
body 

Dif- 
fer- 
ence. 

terial. 

weight. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Gms. 

Dec.  20 

1,657-90 

139.00 

622.40 

2,419.30 

i,O4.v8o 

652.86 

838.3° 

2,536-96 

—117.66 

—  III.  00 

6.66 

The  platform  balance,  with  weighing  arrangements,  shown  in  figure 
46,  was  used  in  this  experiment  for  checking  the  body  weights,  and  in 
the  next  to  the  last  column  of  Table  14  we  have  the  exact  loss  in  weight 
as  recorded  on  this  particular  day  by  this  balance.  As  a  matter  of  fact, 
it  is  seen  that  the  loss  in  weight  as  recorded  by  the  balance  was  in 
grams,  which  differs  somewhat  from  the  amount  computed  from  the 
figures  in  Table  12,  z.  <?.,  164.78  grams.  In  this  connection  it  may  be 
stated  that  the  experimental  routine,  especially  with  reference  to  the 
weighing,  was  not  in  a  satisfactory  condition  on  the  date  on  which  this 
experiment  was  made,  and  consequently  the  corrections  for  the  differ- 
ences in  amount  of  urine  passed  each  day  at  7  a.  m.  before  the  actual 
weighing  account  in  large  measure  for  the  discrepanc)-  noted  above. 

In  Table  14  the  balance  of  intake  and  output  of  material  in  grams 
is  given,  and  from  these  figures  the  loss  of  body  material  is  calcu- 
lated to  be  117.66  grams,  making,  therefore,  an  actual  discrepancy 
between  that  computed  and  that  found  by  the  platform  balance  equal 
to  6.66  grams. 

Subsequent  experience  with  the  platform  balance  has  shown  that 
with  a  perfected  technique  the  agreement  between  the  computed  gain 
or  loss  of  body  material  and  that  actually  found  is  very  close. 

INTAKE  AND  OUTPUT  OF  ENERGY. 


Table  15  summarizes  the  data  regarding  the  intake  and  output  of 
energy  in  the  body  during  this  experiment. 


EXPERIMENT   WITH    MAN.  i 

• 

TABI,E  15. — Intake  and  Output  of  Energy,  Metabolism  Experiment  No.  70. 


Date. 

Heat  of  combustion 
of  food  and  excreta 
as  determined  by 
use  of  the   bomb 
calorimeter. 

(rfV 
Avail- 
able 
energy 

Heat  of  combus- 
tion of  body  ma- 
terial gained  or 
lost    as    calcu- 
lated by  use  of 
factors. 

(h) 

Total 
energy 
from 
body 
material 

(') 
Esti- 
mated 
energy 
from 
mate- 
rial 

C/> 

Heat 
meas- 
ured 
by. 
respi- 

Heat measured 
greater  or  less 
than     esti- 
mated. 

gained 

oxi- 

ration 

(«) 

Food. 

(*) 
Feces. 

(f) 

Urine. 

a-(b+c) 

w 

Pro- 
tein. 

(/) 
Fat. 

(f) 
Gly- 
co- 
gen. 

or 
lost. 

(e+S+e) 

dized 
in  the 
body. 
(d-h) 

calo- 
rim- 
eter. 

(*) 
Amount. 

(I) 
Pro- 
por- 
tion. 

1904- 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Cals. 

Perct. 

Dec.  20 

2,569 

149 

103 

2,317 

-165 

+321 

+  73 

+  229 

2,088 

2,113 

+  25 

+  1.2 

In  this  discussion  the  intake  of  energy  is  the  energy  from  the  mate- 
rial actually  katabolized,  z.  e.,  broken  down  and  oxidized  in  the  body, 
including,  therefore,  not  only  the  energy  of  katabolized  food  but  also 
that  of  the  body  material  lost.  The  output  of  energy  is  that  given 
off  by  the  body  as  heat,  measured  either  as  sensible  heat  by  the  respi- 
ration calorimeter  or  as  heat  of  vaporization  of  water.  The  intake  of 
energy  may  be  measured  in  a  number  of  ways.  First,  we  may  con- 
sider the  intake  as  the  potential  energy  of  the  food  ingested  and  consider 
the  potential  energy  of  the  unoxidized  material  in  the  urine  and  feces 
as  a  part  of  the  output.  Second,  we  may  correct  the  potential  energy 
of  the  food  for  that  of  the  feces  and  urine  by  deducting  the  amount  of 
energy  in  these  latter,  thus  obtaining  the  so-called  ' '  available ' '  energy. 
Without  entering  into  any  discussion  here  as  regards  the  merits  of 
the  two  methods  of  computation,  we  may  proceed  to  the  discussion  of 
Table  15.  The  available  energy  of  the  food  is  calculated  from  the  heat 
of  combustion  of  the  food,  column  (a),  the  heats  of  combustion  of  the 
unoxidized  material  in  the  feces,  column  (£),  and  urine,  column  (c). 
These  quantities  are  taken  from  Tables  6  and  7,  respectively.  As 
previously  explained,  they  are  the  results  of  actual  determinations. 

When  the  available  energy  of  the  food  is  more  than  sufficient  for  the 
needs  of  the  body,  more  or  less  of  the  surplus  food  may  be  stored  as 
body  material,  and  the  quantity  of  energy  in  the  material  so  stored 
must  be  subtracted  from  the  available  energy  of  the  food  to  obtain  the 
energy  of  the  material  actually  metabolized,  which  is  the  energy  of 
intake  here  considered.  On  the  other  hand,  if  the  available  energy  of 
the  food  is  not  sufficient,  the  body  will  draw  upon  its  own  previously 
stored  material,  and  the  amount  of  energy  thus  derived  must  be  added 
to  that  available  from  the  food  to  give  the  total  energy  of  material 
oxidized  in  the  body. 


1 92  A    RESPIRATION   CALORIMETER. 

It  may  happen  that  the  body  will  increase  its  store  of  one  material 
while  drawing  upon  that  of  another.  Thus  the  figures  for  the  experi- 
ment under  discussion  (Table  12)  show  a  gain  of  glycogen  and  fat  at 
the  same  time  with  a  loss  of  protein  in  the  body.  Under  these  circum- 
stances, the  quantity  of  energy  from  body  material  that  is  to  be  added 
to  the  available  energy  of  food  is  the  difference  between  the  energy  of 
material  lost  and  that  of  material  gained. 

CALCULATIONS   OP   ENERGY  OF  BODY   MATERIAL  GAINED   AND   LOST. 

Returning  now  to  the  summary  of  intake  and  output  of  energy  in 
Table  15,  the  total  energy  of  body  material  gained  or  lost,  as  given 
in  column  (^),  is  the  algebraic  sum  of  the  quantities  in  columns  (^), 
(/),  and  (£•) .  These  latter  quantities  are  calculated  from  the  amounts 
of  body  material  gained  or  lost,  as  shown  in  Table  12,  by  use  of  factors 
for  the  heats  of  combustion  per  gram  of  body  materials.  The  factor 
for  protein,  5.65  calories  per  gram,  is  that  for  fat-free  muscular  tissue 
from  which  the  non-proteid  nitrogenous  compounds  have  not  been 
removed.  The  factor  for  fat,  9.54  calories  per  gram,  is  the  average  of 
the  results  of  several  determinations  of  the  heat  of  combustion  of  fat 
from  the  human  body;  and  the  factor  for  glycogen,  4.19  calories  per 
gram,  is  likewise  the  result  determined  by  actual  combustion  of  that 
material.  Applying  these  factors  to  the  amounts  of  body  material 
gained  or  lost,  and  adding  (algebraically)  the  results,  gives  the  total 
amount  of  energy  from  body  material,  as  illustrated  by  the  following 
computations  for  December  20  : 

Protein,      —  29.16  grams  X  5.65  = —  165  calories. 
Fat,  +  33.65  grams  X  9.54  =  -f  320  calories. 

Glycogen,  +  17-34  grams  X  4.19  =  +    73  calories. 

Total  energy  from  body  material  =  +  229  calories. 

The  minus  sign  in  column  (<?)  indicates  that  the  body  has  lost  the 
energy  from  the  amount  potential  in  its  previously  stored  material, 
while  the  plus  sign  in  columns  (/)  and  (g~)  indicates  that  the  energy 
was  potential  in  body  material  stored.  The  total  amount  of  energy 
derived  from  the  body  material  that  was  utilized,  shown  in  column  (A), 
is  therefore  the  difference  between  the  amount  lost  and  the  amount 
stored,  or,  in  other  words,  the  algebraic  sum  of  the  quantities  in  col- 
umns (*),  (/),  and  (£•). 

The  figures  in  column  (z)  represent  the  estimated  amounts  of  energy 
of  the  material  oxidized  in  the  body.  They  are  the  difference  between 
the  quantities  in  column  (of),  the  available  energy  of  the  food,  and  tho.se 
in  column  (A),  the  energy  from  the  body  material  stored.  Since  the 


CONCLUSION.  193 

energy  of  this  stored  material  was  obtained  from  that  of  the  food  in 
excess  of  that  required  to  supply  the  needs  of  the  body,  the  figures  of 
column  (h*)  are  subtracted  from  those  of  column  (d}  to  make  the  total 
energy  of  material  oxidized. 

The  output  of  energy  consists  of  the  heat  given  off  from  the  body 
either  as  sensible  heat  or  heat  of  vaporization  of  water.  Both  quanti- 
ties are  measured  directly  by  the  respiration  calorimeter.  The  figures 
in  column  (/)  show  the  amounts  of  heat  thus  measured.  These  are 
taken  from  column  (g}  in  Table  n.  Theoretically,  the  quantity  for 
intake  should  be  the  same  as  that  of  the  output.  It  would  hardly  be 
expected,  however,  that  results  agreeing  exactly  would  be  obtained. 
Column  (£)  shows  the  difference  between  the  heat  measured  by  the 
respiration  calorimeter  and  the  energy  of  material  oxidized  in  the  body 
as  estimated  from  the  heat  of  combustion  of  food,  feces  and  urine,  and 
that  of  body  material  gained  or  lost.  This  difference  is  expressed  in 
column  (/)  in  percentages  of  the  amounts  in  (/) . 

CONCLUSION. 

Throughout  this  report  the  attempt  has  been  made  to  indicate  the 
experimental  limitations  as  well  as  the  relative  accuracy  of  this  appa- 
ratus. Believing  that  improvement  in  experimental  technique  is  an 
essential  in  increasing  our  knowledge  of  those  processes  of  physiolog- 
ical chemistry  that  have  special  reference  to  the  nutrition  of  man,  we 
have  aimed  in  the  development  of  this  apparatus  to  secure  in  so  far  as 
possible  the  accuracy  of  those  forms  of  physical  apparatus  ordinarily 
designated  as  instruments  of  precision.  The  incidental  errors  of 
manipulation  and  computation  are  by  no  means  wholly  eliminated. 
Indeed,  as  is  to  be  expected  with  an  apparatus  involving  so  many 
mechanical  details,  the  number  of  possible  errors  is  not  inconsiderable. 
We  believe,  however,  that  in  fundamental  principles  and  practical  use 
it  has  proved  as  exact  as  could  well  be  expected  of  an  apparatus  for 
physiological  experimenting. 


2      7770 


THE  UNIVERSITY  LIBRARY 

UNIVERSITY  OF  CALIFORNIA,  SANTA  CRUZ 

SCIENCE  LIBRARY 

This  book  is  due  on  the  last  DATE  stamped  below. 


f  EB  1  0  1971 


1  7 


DEC  15  '87 

DEC  14  1987  WO 


50m-4,'69(J7948s8)2477 


QP121.A9Sci 


3  2106  00259  4874 


